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    NS3/4A Protease Inhibitor Antivirals in Combination with NS5A Protein Inhibitor Antivirals for Hepatitis C

    BOXED WARNING

    Hepatitis B exacerbation

    Use of direct-acting antivirals (DAA), such as ombitasvir and paritaprevir, to treat hepatitis C virus (HCV) infections in patients currently or previously infected with hepatitis B virus (HBV) has been associated with reactivation and exacerbation of the HBV infection. Hepatitis B reactivation has also occurred in patients receiving certain immunosuppressive or chemotherapeutic medications; the risk of HBV reactivation associated with DAA treatment may be increased in these patients. To decrease the risk of reactivating a HBV infection, screen all potential drug recipients for evidence of current or prior HBV infection by measuring hepatitis B surface antigen (HBsAg) and hepatitis B core antibody (anti-HBc). For those patients whose screening reveals serologic evidence of HBV infection, a baseline HBV DNA concentration should be obtained prior to starting ombitasvir; paritaprevir; ritonavir. Continue to monitor coinfected patients during and after treatment for clinical and laboratory signs of hepatitis B exacerbation (i.e., HBsAg, HBV DNA, hepatic enzymes, bilirubin). In addition, instruct patients to immediately report any signs of liver toxicity (e.g., yellow eyes or skin, fatigue, weakness, loss of appetite, nausea, vomiting, or light-colored stools) to their health care provider. If an ombitasvir; paritaprevir; ritonavir recipient develops signs of HBV reactivation, initiate appropriate treatment for HBV infection or consult a physician with expertise in the management of hepatitis infections. The FDA has identified and confirmed 24 cases of hepatitis B exacerbation (including fulminant hepatitis, hepatic failure requiring liver transplant n = 1, and death n = 2) in coinfected patients treated with a DAA-based HCV regimen between November 2013 and July 2016. The exact mechanism is unknown; however, a commonly reported sequence of events included initiation of a DAA-based HCV regimen, rapid drop in HCV RNA to undetectable levels within 1 to 2 weeks of liver enzyme normalization, followed by a rise in HBV DNA (with or without increased transaminases) between treatment weeks 4 and 8. Of the 24 reported cases: 8 discontinued the DAA when transaminases began to rise; 12 received HBV treatment with tenofovir or entecavir; 6 did not receive HBV treatment; and 6 did not report whether HBV treatment was used.

    DEA CLASS

    Rx

    DESCRIPTION

    3 drug oral combination product including a HCV NS5A inhibitor, a NS3/4A protease inhibitor, and a pharmacokinetic enhancer
    For use with ribavirin in the treatment of genotype 4 hepatitis C virus (HCV) infections in patients without cirrhosis or with compensated cirrhosis
    Contraindicated in patients with moderate to severe hepatic disease

    COMMON BRAND NAMES

    Technivie

    HOW SUPPLIED

    Technivie Oral Tab: 12.5-75-50mg

    DOSAGE & INDICATIONS

    For the treatment of genotype 4 chronic hepatitis C infection in patients without cirrhosis or with compensated cirrhosis.
    Oral dosage
    Adults 75 kg or more

    Two fixed-dose combination tablets containing ombitasvir; paritaprevir; ritonavir (12.5/75/50 mg per tablet) PO once daily in the morning with ribavirin 600 mg PO twice daily. Consideration may be given to administering two fixed-dose combination tablets once daily without ribavirin for non-cirrhotic treatment-naive patients who are unable to tolerate ribavirin. Administer for 12 weeks.

    Adults less than 75 kg

    Two fixed-dose combination tablets containing ombitasvir; paritaprevir; ritonavir (12.5/75/50 mg per tablet) PO once daily in the morning with ribavirin 500 mg PO twice daily. Consideration may be given to administering two fixed-dose combination tablets once daily without ribavirin for non-cirrhotic treatment-naive patients who are unable to tolerate ribavirin. Administer for 12 weeks.

    MAXIMUM DOSAGE

    Adults

    25 mg/day PO for ombitasvir; 150 mg/day PO for paritaprevir; 100 mg/day PO for ritonavir

    Geriatric

    25 mg/day PO for ombitasvir; 150 mg/day PO for paritaprevir; 100 mg/day PO for ritonavir

    Adolescents

    Safety and efficacy not established.

    Children

    Safety and efficacy not established.

    Infants

    Safety and efficacy not established.

    Neonates

    Safety and efficacy not established.

    DOSING CONSIDERATIONS

    Hepatic Impairment

    Use is contraindicated in patients with moderate to severe hepatic impairment (Child-Pugh Class B and C). In addition, the manufacturer recommends treatment be avoided in patients with decompensated cirrhosis. No dosage adjustments are needed for mild hepatic impairment (Child-Pugh Class A).

    Renal Impairment

    Specific guidelines for dosage adjustments in renal impairment are not available; it appears that no dosage adjustments are needed.

    ADMINISTRATION

    Oral Administration

    Administer with a meal, regardless of fat or caloric content.

    STORAGE

    Technivie:
    - Store below 86 degrees F

    CONTRAINDICATIONS / PRECAUTIONS

    Use with ribavirin

    Ombitasvir; paritaprevir; ritonavir is recommended for use with ribavirin; therefore, any contraindication to ribavirin will also apply to the combination regimen. See the ribavirin monograph for additional information. In addition, complex interactions are likely with ombitasvir; paritaprevir; ritonavir. According to the manufacturer, use of the drug is contraindicated with moderate to strong inducers of CYP3A4 and with CYP3A4 substrates for which elevated plasma concentrations may result in serious adverse events. Evaluate the medication profile of all potential drug recipients prior to and during treatment with ombitasvir; paritaprevir; ritonavir.

    Hepatic disease

    Ombitasvir; paritaprevir; ritonavir is contraindicated in patients with moderate to severe hepatic disease (Child-Pugh Class B and C) due to the potential risk of toxicity. In addition, use must be avoided in patients with decompensated cirrhosis. There are no restrictions for use in patients with mild hepatic impairment (Child-Pugh A). Health care providers are advised to closely monitor patients with compensated cirrhosis for signs and symptoms of hepatic decompensation, such as ascites, hepatic encephalopathy, and variceal hemorrhage. Drug recipients should be counseled to immediately contact their health care provider if they develop fatigue, weakness, loss of appetite, nausea and vomiting, yellow eyes or skin, confusion, abdominal swelling, or light-colored stools, as these may be signs of liver toxicity. Liver function tests (including direct bilirubin concentrations) are recommended prior to initiating treatment, during the first 4 weeks of therapy, and as clinically indicated thereafter. If ALT is elevated above baseline, repeat testing and monitor closely. Consider treatment discontinuation if ALT concentrations remain persistently greater than 10-times the upper limit of normal (ULN). Discontinuation is also recommended if ALT elevation is accompanied by signs or symptoms of liver inflammation or increasing conjugated bilirubin, alkaline phosphatase, or INR. During clinical trials of ombitasvir; paritaprevir; ritonavir with and without ribavirin and dasabuvir, ALT elevations greater than 5-times the ULN occurred in approximately 1% of patients. Elevations typically developed during the first 4 weeks of treatment, were usually asymptomatic, and declined within 2 to 8 weeks of onset with continued administration of the drug. Of note, ALT elevations occurred significantly more often in female patients receiving ethinyl estradiol containing medications; therefore, concurrent use of these medications is not recommended. Since December 2014, at least 26 cases of serious liver injury (hepatic decompensation, n = 16; hepatic failure resulting in liver transplant or death, n = 10) have been reported to the FDA as possibly related to ombitasvir; paritaprevir; ritonavir containing medications. In most cases, toxicity occurred in patients with underlying advanced cirrhosis and developed within 1 to 4 weeks of starting therapy; some of the reported cases involved patients for whom use of the drug is contraindicated or not recommended. To promote safe use, the FDA has issued a Drug Safety Communication alerting health care providers and patients of the potential risk for liver toxicity. Both health care providers and patients are advised to monitor for signs and symptoms of liver injury. If liver injury develops, patients should immediately contact their prescriber; patients are advised not to stop taking the medication without first talking to their prescriber.

    Hepatitis C and HIV coinfection

    Patients with hepatitis C and HIV coinfection who are receiving ombitasvir; paritaprevir; ritonavir should also be on a suppressive antiretroviral drug regimen to reduce the risk of HIV-1 protease inhibitor drug resistance. Ritonavir is a HIV-1 protease inhibitor and can select for HIV-1 protease inhibitor resistance-associated substitutions. HIV treatment guidelines recommend all patients presenting with HIV infection undergo testing for hepatitis C, with continued annual screening advised for those persons considered high risk for acquiring hepatitis C. If hepatitis C and HIV coinfection is identified, consider treating both viral infections concurrently. For most patients, the benefits of concurrent therapy outweighs the potential risks (i.e., drug-induced hepatic injury, complex drug interactions, overlapping toxicities); therefore, it is recommended to initiate a fully suppressive antiretroviral (ARV) therapy and a hepatitis C regimen in all coinfected patients regardless of CD4 count. However, for antiretroviral naive patients with CD4 counts greater than 500 cells/mm3, consideration may be given to deferring ARV until the hepatitis C treatment regimen has been completed. Conversely, for patients with CD4 counts less than 200 cells/mm3, consider delaying initiation of the hepatitis C treatment regimen until the patient is stable on fully suppressive ARV regimen. Instruct coinfected patients to avoid consuming alcohol, and offer vaccinations against hepatitis A and hepatitis B as appropriate.

    Contraception requirements, male-mediated teratogenicity, pregnancy, pregnancy testing

    There are no well controlled studies evaluating use of ombitasvir; paritaprevir; ritonavir in pregnant women. In animal studies involving mice, rats and rabbits, no evidence of teratogenicity was observed with ombitasvir, paritaprevir, or ritonavir at exposures higher than the recommended clinical dose. Ombitasvir; paritaprevir; ritonavir is contraindicated for use in pregnant females and males whose female partners are pregnant if administered in combination with ribavirin. Use of ribavirin may cause birth defects and death of the exposed fetus. Ribavirin therapy also may cause male-mediated teratogenicity and is contraindicated for use during pregnancy (FDA pregnancy risk category X), in females who may become pregnant, or in men whose female partners are pregnant. Studies of ribavirin indicate teratogenic (e.g., malformations of skull, palate, eye, jaw, limbs, skeleton, and GI tract) or embryocidal properties in all of the animal species tested. Patients and their partners are required use 2 reliable forms of effective contraception (e.g., intrauterine devices, barrier methods) during ribavirin treatment and for 6 months post-therapy. Patients who are not willing to adhere to the strict contraception requirements should not receive treatment with ribavirin. Females must also undergo pregnancy testing prior to initiation of therapy, monthly during therapy, and for 6 months post-therapy. To monitor maternal-fetal outcomes of pregnancies in female patients and female partners of male patients exposed to ribavirin during treatment and for 6 months following cessation of treatment, health care providers are encouraged to report any cases to the Ribavirin Pregnancy Registry; telephone (800) 593-2214.

    Breast-feeding

    According to the manufacturer, it is not known if ombitasvir; paritaprevir; ritonavir or their metabolites are excreted in human milk. It is also unknown if ribavirin is excreted in human breast milk; however, ribavirin has been shown to be toxic to nursing animals. For lactating women who require concurrent treatment with ribavirin, a decision must be made whether to discontinue nursing or discontinue therapy. Consider the benefits of breast-feeding, the risk of infant drug exposure, and the risk of an untreated or inadequately treated condition. If a breast-feeding infant experiences an adverse effect related to a maternally ingested drug, health care providers are encouraged to report the adverse effect to the FDA.

    Hepatitis B exacerbation

    Use of direct-acting antivirals (DAA), such as ombitasvir and paritaprevir, to treat hepatitis C virus (HCV) infections in patients currently or previously infected with hepatitis B virus (HBV) has been associated with reactivation and exacerbation of the HBV infection. Hepatitis B reactivation has also occurred in patients receiving certain immunosuppressive or chemotherapeutic medications; the risk of HBV reactivation associated with DAA treatment may be increased in these patients. To decrease the risk of reactivating a HBV infection, screen all potential drug recipients for evidence of current or prior HBV infection by measuring hepatitis B surface antigen (HBsAg) and hepatitis B core antibody (anti-HBc). For those patients whose screening reveals serologic evidence of HBV infection, a baseline HBV DNA concentration should be obtained prior to starting ombitasvir; paritaprevir; ritonavir. Continue to monitor coinfected patients during and after treatment for clinical and laboratory signs of hepatitis B exacerbation (i.e., HBsAg, HBV DNA, hepatic enzymes, bilirubin). In addition, instruct patients to immediately report any signs of liver toxicity (e.g., yellow eyes or skin, fatigue, weakness, loss of appetite, nausea, vomiting, or light-colored stools) to their health care provider. If an ombitasvir; paritaprevir; ritonavir recipient develops signs of HBV reactivation, initiate appropriate treatment for HBV infection or consult a physician with expertise in the management of hepatitis infections. The FDA has identified and confirmed 24 cases of hepatitis B exacerbation (including fulminant hepatitis, hepatic failure requiring liver transplant n = 1, and death n = 2) in coinfected patients treated with a DAA-based HCV regimen between November 2013 and July 2016. The exact mechanism is unknown; however, a commonly reported sequence of events included initiation of a DAA-based HCV regimen, rapid drop in HCV RNA to undetectable levels within 1 to 2 weeks of liver enzyme normalization, followed by a rise in HBV DNA (with or without increased transaminases) between treatment weeks 4 and 8. Of the 24 reported cases: 8 discontinued the DAA when transaminases began to rise; 12 received HBV treatment with tenofovir or entecavir; 6 did not receive HBV treatment; and 6 did not report whether HBV treatment was used.

    Infertility

    In animal studies, ribavirin was associated with testicular degeneration and infertility; therefore, caution is advised when administering ombitasvir; paritaprevir; ritonavir with ribavirin to males. Testicular degeneration appears to be reversible after stopping ribavirin with recovery occurring within 1 or 2 spermatogenesis cycles.

    Cardiac disease, cerebrovascular disease

    Prior to administering ombitasvir; paritaprevir; ritonavir with ribavirin, assess potential drug recipients for underlying cardiac disease. The anemia associated with ribavirin therapy may result in deterioration in cardiac function and exacerbation of the symptoms of coronary artery disease or cerebrovascular disease. If there is any deterioration in cardiac status, therapy should be suspended or discontinued. Because cardiac disease (e.g., angina or congestive heart failure) may be worsened by drug-induced anemia, patients with a history of significant or unstable cardiac disease should not use ribavirin therapy. Those patients with a history of myocardial infarction or previous or current cardiac arrhythmias should be closely monitored; fatal and nonfatal myocardial infarctions have been reported in patients with ribavirin-induced anemia.

    Anticoagulant therapy

    Caution is advised when prescribing ombitasvir; paritaprevir; ritonavir to patients receiving concurrent anticoagulant therapy, specifically warfarin. Fluctuations in International Normalized Ratio (INR) have been observed in warfarin recipients who were also receiving treatment for hepatitis C virus (HCV) infections. It is recommended to closely monitor these patients for changes in INR both during and after discontinuation of the HCV treatment regimen.

    ADVERSE REACTIONS

    Severe

    suicidal ideation / Delayed / 0-11.0
    atrial fibrillation / Early / 0-9.0
    erythema multiforme / Delayed / Incidence not known
    angioedema / Rapid / Incidence not known
    serious hypersensitivity reactions or anaphylaxis / Rapid / Incidence not known
    hepatic failure / Delayed / Incidence not known
    hepatitis B exacerbation / Delayed / Incidence not known

    Moderate

    hyperbilirubinemia / Delayed / 5.0-40.0
    erythema / Early / 0-13.0
    contact dermatitis / Delayed / 0-13.0
    skin ulcer / Delayed / 0-13.0
    psoriasis / Delayed / 0-13.0
    mania / Early / 0-11.0
    dyspnea / Early / 0-11.0
    depression / Delayed / 0-11.0
    angina / Early / 0-9.0
    palpitations / Early / 0-9.0
    hypertension / Early / 0-9.0
    hypotension / Rapid / 0-9.0
    chest pain (unspecified) / Early / 0-9.0
    edema / Delayed / 6.0-6.0
    memory impairment / Delayed / 6.0-6.0
    peripheral edema / Delayed / 6.0-6.0
    ascites / Delayed / 0-1.0
    jaundice / Delayed / 0-1.0
    elevated hepatic enzymes / Delayed / 1.0-1.0
    anemia / Delayed / 0-1.0

    Mild

    asthenia / Delayed / 25.0-29.0
    fatigue / Early / 7.0-25.0
    headache / Early / 23.0-23.0
    weakness / Early / 0-17.0
    myalgia / Early / 0-17.0
    back pain / Delayed / 0-17.0
    arthralgia / Delayed / 0-17.0
    pruritus / Rapid / 5.0-16.0
    insomnia / Early / 5.0-14.0
    nausea / Early / 9.0-14.0
    maculopapular rash / Early / 0-13.0
    xerosis / Delayed / 0-13.0
    rash / Early / 0-13.0
    urticaria / Rapid / 0-13.0
    photosensitivity / Delayed / 0-13.0
    agitation / Early / 0-11.0
    anxiety / Delayed / 0-11.0
    dizziness / Early / 0-11.0
    irritability / Delayed / 0-11.0
    abdominal pain / Early / 9.0-9.0
    cough / Delayed / 7.0-7.0
    anorexia / Delayed / 6.0-6.0
    vomiting / Early / 6.0-6.0

    DRUG INTERACTIONS

    Abacavir: (Moderate) Caution is advised when administering abacavir and ritonavir concurrently. Ritonavir appears to induce glucuronosyl transferase, and therefore, has the potential to reduce plasma concentrations of drugs that undergo glucuronidation, such as abacavir. The clinical significance of the potential for this interaction is unknown.
    Abacavir; Dolutegravir; Lamivudine: (Moderate) Caution and close monitoring are advised if these drugs are administered together. Concurrent administration of dolutegravir with ombitasvir may result in elevated dolutegravir plasma concentrations. Dolutegravir is a substrate of uridine glucuronyltransferase (UGT). Ombitasvir inhibits UGT1A1. (Moderate) Caution and close monitoring are advised if these drugs are administered together. Concurrent administration of dolutegravir with paritaprevir may result in elevated dolutegravir plasma concentrations. Dolutegravir is a substrate of uridine glucuronyltransferase (UGT) and the breast cancer resistance protein (BCRP). Paritaprevir inhibits UGT1A1 and BCRP. (Moderate) Caution is advised when administering abacavir and ritonavir concurrently. Ritonavir appears to induce glucuronosyl transferase, and therefore, has the potential to reduce plasma concentrations of drugs that undergo glucuronidation, such as abacavir. The clinical significance of the potential for this interaction is unknown.
    Abacavir; Lamivudine, 3TC: (Moderate) Caution is advised when administering abacavir and ritonavir concurrently. Ritonavir appears to induce glucuronosyl transferase, and therefore, has the potential to reduce plasma concentrations of drugs that undergo glucuronidation, such as abacavir. The clinical significance of the potential for this interaction is unknown.
    Abacavir; Lamivudine, 3TC; Zidovudine, ZDV: (Moderate) Caution is advised when administering abacavir and ritonavir concurrently. Ritonavir appears to induce glucuronosyl transferase, and therefore, has the potential to reduce plasma concentrations of drugs that undergo glucuronidation, such as abacavir. The clinical significance of the potential for this interaction is unknown. (Minor) Since ritonavir induces glucuronidation, there is the potential for reduction in zidovudine, ZDV plasma concentrations during concurrent therapy with ritonavir. When coadministered with ritonavir, the AUC and Cmax of zidovudine, ZDV are decreased by 12% and 27%. The clinical significance of this interaction is unknown.
    Abemaciclib: (Major) If coadministration with ritonavir is necessary, reduce the dose of abemaciclib to 100 mg PO twice daily in patients on either of the recommended starting doses of either 200 mg or 150 mg twice daily. In patients who have had already had a dose reduction to 100 mg twice daily due to adverse reactions, further reduce the dose of abemaciclib to 50 mg PO twice daily. Discontinue abemaciclib for patients unable to tolerate 50 mg twice daily. If ritonavir is discontinued, increase the dose of abemaciclib to the original dose after 3 to 5 half-lives of ritonavir. Abemaciclib is a CYP3A4 substrate and ritonavir is a strong CYP3A4 inhibitor. Coadministration with another strong CYP3A4 inhibitor increased the relative potency adjusted unbound AUC of abemaciclib plus its active metabolites (M2, M18, and M20) by 2.5-fold in cancer patients.
    Acalabrutinib: (Major) Avoid the concomitant use of acalabrutinib and ritonavir; significantly increased acalabrutinib exposure may occur. Acalabrutinib is a CYP3A4 substrate; ritonavir is a strong CYP3A4 inhibitor. In healthy subjects, the Cmax and AUC values of acalabrutinib were increased by 3.9-fold and 5.1-fold, respectively, when acalabrutinib was coadministered with another strong inhibitor for 5 days. (Moderate) Coadministration of acalabrutinib and ombitasvir, paritaprevir, ritonavir may increase the exposure and the risk of toxicity of ombitasvir, paritaprevir, ritonavir. Acalabrutinib is a substrate and inhibitor of the breast cancer resistance protein (BCRP) transporter in vitro; it may inhibit intestinal BCRP. Ombitasvir is a BCRP transporter substrate and paritaprevir is a substrate and inhibitor of BCRP.
    Acarbose: (Moderate) New onset diabetes mellitus, exacerbation of diabetes mellitus, and hyperglycemia due to insulin resistance have been reported with use of anti-retroviral protease inhibitors.
    Acebutolol: (Moderate) Cardiac and neurologic events have been reported when ritonavir was concurrently administered with beta-blockers.
    Acetaminophen: (Moderate) Concurrent administration of acetaminophen with ritonavir may result in elevated acetaminophen plasma concentrations and subsequent adverse events. Acetaminophen is metabolized by the hepatic isoenzyme CYP3A4; ritonavir is an inhibitor of this enzyme. Caution and close monitoring are advised if these drugs are administered together.
    Acetaminophen; Aspirin, ASA; Caffeine: (Moderate) Concurrent administration of acetaminophen with ritonavir may result in elevated acetaminophen plasma concentrations and subsequent adverse events. Acetaminophen is metabolized by the hepatic isoenzyme CYP3A4; ritonavir is an inhibitor of this enzyme. Caution and close monitoring are advised if these drugs are administered together.
    Acetaminophen; Butalbital: (Major) Concurrent use of ritonavir with phenobarbital or other barbiturates should be done cautiously. Increased doses of anticonvulsants may be required due metabolism induction by ritonavir. However, since these anticonvulsants are hepatic enzyme inducing drugs, increased metabolism of protease inhibitors may occur, leading to decreased antiretroviral efficacy. Close monitoring of drug concentrations and/or therapeutic and adverse effects is required. (Moderate) Concurrent administration of acetaminophen with ritonavir may result in elevated acetaminophen plasma concentrations and subsequent adverse events. Acetaminophen is metabolized by the hepatic isoenzyme CYP3A4; ritonavir is an inhibitor of this enzyme. Caution and close monitoring are advised if these drugs are administered together.
    Acetaminophen; Butalbital; Caffeine: (Major) Concurrent use of ritonavir with phenobarbital or other barbiturates should be done cautiously. Increased doses of anticonvulsants may be required due metabolism induction by ritonavir. However, since these anticonvulsants are hepatic enzyme inducing drugs, increased metabolism of protease inhibitors may occur, leading to decreased antiretroviral efficacy. Close monitoring of drug concentrations and/or therapeutic and adverse effects is required. (Moderate) Concurrent administration of acetaminophen with ritonavir may result in elevated acetaminophen plasma concentrations and subsequent adverse events. Acetaminophen is metabolized by the hepatic isoenzyme CYP3A4; ritonavir is an inhibitor of this enzyme. Caution and close monitoring are advised if these drugs are administered together.
    Acetaminophen; Butalbital; Caffeine; Codeine: (Major) Concurrent use of ritonavir with phenobarbital or other barbiturates should be done cautiously. Increased doses of anticonvulsants may be required due metabolism induction by ritonavir. However, since these anticonvulsants are hepatic enzyme inducing drugs, increased metabolism of protease inhibitors may occur, leading to decreased antiretroviral efficacy. Close monitoring of drug concentrations and/or therapeutic and adverse effects is required. (Moderate) Concomitant use of codeine with ritonavir may alter codeine plasma concentrations, resulting in an unpredictable effect such as reduced efficacy or symptoms of opioid withdrawal or prolonged opioid adverse reactions, including hypotension, respiratory depression, profound sedation, coma, and death. It is recommended to avoid this combination when codeine is being used for cough. If coadministration is necessary, monitor patients closely at frequent intervals and consider a dosage adjustment of codeine until stable drug effects are achieved. Discontinuation of ritonavir could alter codeine plasma concentrations, resulting in an unpredictable effect such as prolonged opioid adverse reactions or decreased opioid efficacy, and potentially lead to a withdrawal syndrome in those with physical dependence to codeine. If ritonavir is discontinued, monitor the patient carefully and consider adjusting the opioid dosage if appropriate. Codeine is primarily metabolized by CYP2D6 to morphine, and by CYP3A4 to norcodeine; norcodeine does not have analgesic properties. Ritonavir is a strong inhibitor of CYP3A4 and a weak inhibitor of CYP2D6. CYP3A4 inhibitors may increase codeine-related adverse effects while CYP2D6 inhibitors may reduce efficacy. (Moderate) Concurrent administration of acetaminophen with ritonavir may result in elevated acetaminophen plasma concentrations and subsequent adverse events. Acetaminophen is metabolized by the hepatic isoenzyme CYP3A4; ritonavir is an inhibitor of this enzyme. Caution and close monitoring are advised if these drugs are administered together.
    Acetaminophen; Caffeine: (Moderate) Concurrent administration of acetaminophen with ritonavir may result in elevated acetaminophen plasma concentrations and subsequent adverse events. Acetaminophen is metabolized by the hepatic isoenzyme CYP3A4; ritonavir is an inhibitor of this enzyme. Caution and close monitoring are advised if these drugs are administered together.
    Acetaminophen; Caffeine; Dihydrocodeine: (Moderate) Concomitant use of dihydrocodeine with ritonavir may increase dihydrocodeine plasma concentrations, resulting in greater metabolism by CYP2D6, increased dihydromorphine concentrations, and prolonged opioid adverse reactions, including hypotension, respiratory depression, profound sedation, coma, and death. If coadministration is necessary, monitor patients closely at frequent intervals and consider a dosage reduction of dihydrocodeine until stable drug effects are achieved. Discontinuation of ritonavir could decrease dihydrocodeine plasma concentrations, decrease opioid efficacy, and potentially lead to a withdrawal syndrome in those with physical dependence to dihydrocodeine. If ritonavir is discontinued, monitor the patient carefully and consider increasing the opioid dosage if appropriate. Ritonavir is a strong inhibitor of CYP3A4, an isoenzyme partially responsible for the metabolism of dihydrocodeine. (Moderate) Concurrent administration of acetaminophen with ritonavir may result in elevated acetaminophen plasma concentrations and subsequent adverse events. Acetaminophen is metabolized by the hepatic isoenzyme CYP3A4; ritonavir is an inhibitor of this enzyme. Caution and close monitoring are advised if these drugs are administered together.
    Acetaminophen; Caffeine; Magnesium Salicylate; Phenyltoloxamine: (Moderate) Concurrent administration of acetaminophen with ritonavir may result in elevated acetaminophen plasma concentrations and subsequent adverse events. Acetaminophen is metabolized by the hepatic isoenzyme CYP3A4; ritonavir is an inhibitor of this enzyme. Caution and close monitoring are advised if these drugs are administered together.
    Acetaminophen; Caffeine; Phenyltoloxamine; Salicylamide: (Moderate) Concurrent administration of acetaminophen with ritonavir may result in elevated acetaminophen plasma concentrations and subsequent adverse events. Acetaminophen is metabolized by the hepatic isoenzyme CYP3A4; ritonavir is an inhibitor of this enzyme. Caution and close monitoring are advised if these drugs are administered together.
    Acetaminophen; Chlorpheniramine; Dextromethorphan; Phenylephrine: (Moderate) Concurrent administration of acetaminophen with ritonavir may result in elevated acetaminophen plasma concentrations and subsequent adverse events. Acetaminophen is metabolized by the hepatic isoenzyme CYP3A4; ritonavir is an inhibitor of this enzyme. Caution and close monitoring are advised if these drugs are administered together. (Moderate) Concurrent administration of chlorpheniramine with ritonavir may result in elevated plasma concentrations of chlorpheniramine. Chlorpheniramine is metabolized by the hepatic isoenzyme CYP2D6; ritonavir is an inhibitor of this enzyme. Monitor for adverse effects if these drugs are administered together.
    Acetaminophen; Chlorpheniramine; Dextromethorphan; Pseudoephedrine: (Moderate) Concurrent administration of acetaminophen with ritonavir may result in elevated acetaminophen plasma concentrations and subsequent adverse events. Acetaminophen is metabolized by the hepatic isoenzyme CYP3A4; ritonavir is an inhibitor of this enzyme. Caution and close monitoring are advised if these drugs are administered together. (Moderate) Concurrent administration of chlorpheniramine with ritonavir may result in elevated plasma concentrations of chlorpheniramine. Chlorpheniramine is metabolized by the hepatic isoenzyme CYP2D6; ritonavir is an inhibitor of this enzyme. Monitor for adverse effects if these drugs are administered together.
    Acetaminophen; Chlorpheniramine; Phenylephrine; Phenyltoloxamine: (Moderate) Concurrent administration of acetaminophen with ritonavir may result in elevated acetaminophen plasma concentrations and subsequent adverse events. Acetaminophen is metabolized by the hepatic isoenzyme CYP3A4; ritonavir is an inhibitor of this enzyme. Caution and close monitoring are advised if these drugs are administered together. (Moderate) Concurrent administration of chlorpheniramine with ritonavir may result in elevated plasma concentrations of chlorpheniramine. Chlorpheniramine is metabolized by the hepatic isoenzyme CYP2D6; ritonavir is an inhibitor of this enzyme. Monitor for adverse effects if these drugs are administered together.
    Acetaminophen; Codeine: (Moderate) Concomitant use of codeine with ritonavir may alter codeine plasma concentrations, resulting in an unpredictable effect such as reduced efficacy or symptoms of opioid withdrawal or prolonged opioid adverse reactions, including hypotension, respiratory depression, profound sedation, coma, and death. It is recommended to avoid this combination when codeine is being used for cough. If coadministration is necessary, monitor patients closely at frequent intervals and consider a dosage adjustment of codeine until stable drug effects are achieved. Discontinuation of ritonavir could alter codeine plasma concentrations, resulting in an unpredictable effect such as prolonged opioid adverse reactions or decreased opioid efficacy, and potentially lead to a withdrawal syndrome in those with physical dependence to codeine. If ritonavir is discontinued, monitor the patient carefully and consider adjusting the opioid dosage if appropriate. Codeine is primarily metabolized by CYP2D6 to morphine, and by CYP3A4 to norcodeine; norcodeine does not have analgesic properties. Ritonavir is a strong inhibitor of CYP3A4 and a weak inhibitor of CYP2D6. CYP3A4 inhibitors may increase codeine-related adverse effects while CYP2D6 inhibitors may reduce efficacy. (Moderate) Concurrent administration of acetaminophen with ritonavir may result in elevated acetaminophen plasma concentrations and subsequent adverse events. Acetaminophen is metabolized by the hepatic isoenzyme CYP3A4; ritonavir is an inhibitor of this enzyme. Caution and close monitoring are advised if these drugs are administered together.
    Acetaminophen; Dextromethorphan: (Moderate) Concurrent administration of acetaminophen with ritonavir may result in elevated acetaminophen plasma concentrations and subsequent adverse events. Acetaminophen is metabolized by the hepatic isoenzyme CYP3A4; ritonavir is an inhibitor of this enzyme. Caution and close monitoring are advised if these drugs are administered together.
    Acetaminophen; Dextromethorphan; Doxylamine: (Moderate) Concurrent administration of acetaminophen with ritonavir may result in elevated acetaminophen plasma concentrations and subsequent adverse events. Acetaminophen is metabolized by the hepatic isoenzyme CYP3A4; ritonavir is an inhibitor of this enzyme. Caution and close monitoring are advised if these drugs are administered together.
    Acetaminophen; Dextromethorphan; Guaifenesin; Phenylephrine: (Moderate) Concurrent administration of acetaminophen with ritonavir may result in elevated acetaminophen plasma concentrations and subsequent adverse events. Acetaminophen is metabolized by the hepatic isoenzyme CYP3A4; ritonavir is an inhibitor of this enzyme. Caution and close monitoring are advised if these drugs are administered together.
    Acetaminophen; Dextromethorphan; Phenylephrine: (Moderate) Concurrent administration of acetaminophen with ritonavir may result in elevated acetaminophen plasma concentrations and subsequent adverse events. Acetaminophen is metabolized by the hepatic isoenzyme CYP3A4; ritonavir is an inhibitor of this enzyme. Caution and close monitoring are advised if these drugs are administered together.
    Acetaminophen; Dextromethorphan; Pseudoephedrine: (Moderate) Concurrent administration of acetaminophen with ritonavir may result in elevated acetaminophen plasma concentrations and subsequent adverse events. Acetaminophen is metabolized by the hepatic isoenzyme CYP3A4; ritonavir is an inhibitor of this enzyme. Caution and close monitoring are advised if these drugs are administered together.
    Acetaminophen; Dichloralphenazone; Isometheptene: (Moderate) Concurrent administration of acetaminophen with ritonavir may result in elevated acetaminophen plasma concentrations and subsequent adverse events. Acetaminophen is metabolized by the hepatic isoenzyme CYP3A4; ritonavir is an inhibitor of this enzyme. Caution and close monitoring are advised if these drugs are administered together.
    Acetaminophen; Diphenhydramine: (Moderate) Concurrent administration of acetaminophen with ritonavir may result in elevated acetaminophen plasma concentrations and subsequent adverse events. Acetaminophen is metabolized by the hepatic isoenzyme CYP3A4; ritonavir is an inhibitor of this enzyme. Caution and close monitoring are advised if these drugs are administered together. (Moderate) Concurrent administration of diphenhydramine with ritonavir may result in elevated plasma concentrations of diphenhydramine. Diphenhydramine is a CYP2D6 substrate, and ritonavir is a CYP2D6 inhibitor. Caution and close monitoring are advised if these drugs are administered together.
    Acetaminophen; Guaifenesin; Phenylephrine: (Moderate) Concurrent administration of acetaminophen with ritonavir may result in elevated acetaminophen plasma concentrations and subsequent adverse events. Acetaminophen is metabolized by the hepatic isoenzyme CYP3A4; ritonavir is an inhibitor of this enzyme. Caution and close monitoring are advised if these drugs are administered together.
    Acetaminophen; Hydrocodone: (Moderate) Concomitant use of hydrocodone with ritonavir may increase hydrocodone plasma concentrations and prolong opioid adverse reactions, including hypotension, respiratory depression, profound sedation, coma, and death. It is recommended to avoid this combination when hydrocodone is being used for cough. If coadministration is necessary, monitor patients closely at frequent intervals and consider a dosage reduction of hydrocodone until stable drug effects are achieved. Discontinuation of ritonavir could decrease hydrocodone plasma concentrations, decrease opioid efficacy, and potentially lead to a withdrawal syndrome in those with physical dependence to hydrocodone. If ritonavir is discontinued, monitor the patient carefully and consider increasing the opioid dosage if appropriate. Hydrocodone is a substrate for CYP3A4 and CYP2D6. Ritonavir is a strong inhibitor of CYP3A4 and also inhibits CYP2D6. (Moderate) Concurrent administration of acetaminophen with ritonavir may result in elevated acetaminophen plasma concentrations and subsequent adverse events. Acetaminophen is metabolized by the hepatic isoenzyme CYP3A4; ritonavir is an inhibitor of this enzyme. Caution and close monitoring are advised if these drugs are administered together.
    Acetaminophen; Oxycodone: (Moderate) Concurrent administration of acetaminophen with ritonavir may result in elevated acetaminophen plasma concentrations and subsequent adverse events. Acetaminophen is metabolized by the hepatic isoenzyme CYP3A4; ritonavir is an inhibitor of this enzyme. Caution and close monitoring are advised if these drugs are administered together. (Moderate) Consider a reduced dose of oxycodone with frequent monitoring for respiratory depression and sedation if concurrent use of ritonavir is necessary. If ritonavir is discontinued, consider increasing the oxycodone dose until stable drug effects are achieved and monitor for evidence of opioid withdrawal. Oxycodone is a CYP3A4 substrate, and coadministration with a strong CYP3A4 inhibitor like ritonavir can increase oxycodone exposure resulting in increased or prolonged opioid effects including fatal respiratory depression, particularly when an inhibitor is added to a stable dose of oxycodone. If ritonavir is discontinued, oxycodone plasma concentrations will decrease resulting in reduced efficacy of the opioid and potential withdrawal syndrome in a patient who has developed physical dependence to oxycodone.
    Acetaminophen; Pentazocine: (Moderate) Concurrent administration of acetaminophen with ritonavir may result in elevated acetaminophen plasma concentrations and subsequent adverse events. Acetaminophen is metabolized by the hepatic isoenzyme CYP3A4; ritonavir is an inhibitor of this enzyme. Caution and close monitoring are advised if these drugs are administered together.
    Acetaminophen; Propoxyphene: (Moderate) Concurrent administration of acetaminophen with ritonavir may result in elevated acetaminophen plasma concentrations and subsequent adverse events. Acetaminophen is metabolized by the hepatic isoenzyme CYP3A4; ritonavir is an inhibitor of this enzyme. Caution and close monitoring are advised if these drugs are administered together. (Moderate) Due to effects on microsomal isoenzymes responsible for hepatic metabolism, ritonavir may alter the response and/or increase the AUC of opiate analgesics. Concurrent use of ritonavir and propoxyphene is not recommended, due the increased formation of the neurotoxic metabolites of propoxyphene. Also, propoxyphene is a substrate/inhibitor of CYP3A4. Increased serum concentrations of propoxyphene can occur from concurrent use of ritonavir, a CYP3A4 inhibitor. A reduced dosage of propoxyphene may be needed. Monitor for CNS and respiratory depression.
    Acetaminophen; Pseudoephedrine: (Moderate) Concurrent administration of acetaminophen with ritonavir may result in elevated acetaminophen plasma concentrations and subsequent adverse events. Acetaminophen is metabolized by the hepatic isoenzyme CYP3A4; ritonavir is an inhibitor of this enzyme. Caution and close monitoring are advised if these drugs are administered together.
    Acetaminophen; Tramadol: (Major) Tramadol is primarily metabolized by CYP2D6 and CYP3A4; drugs that inhibit these enzymes, such as ritonavir, may decrease the metabolism of tramadol. This may result in a decreased concentration of the active metabolite (O-desmethyltramadol) leading to decreased analgesic effects and possibly increased side effects (seizures and serotonin syndrome) due to higher tramadol concentrations. (Moderate) Concurrent administration of acetaminophen with ritonavir may result in elevated acetaminophen plasma concentrations and subsequent adverse events. Acetaminophen is metabolized by the hepatic isoenzyme CYP3A4; ritonavir is an inhibitor of this enzyme. Caution and close monitoring are advised if these drugs are administered together.
    Adefovir: (Major) Patients who are concurrently taking adefovir with antiretrovirals like the protease inhibitors, are at risk of developing lactic acidosis and severe hepatomegaly with steatosis. Lactic acidosis and severe hepatomegaly with steatosis, including fatal cases, have been reported with the use of nucleoside analogs alone or in combination with antiretrovirals. A majority of these cases have been in women; obesity and prolonged nucleoside exposure may also be risk factors. Particular caution should be exercised when administering nucleoside analogs to any patient with known risk factors for hepatic disease; however, cases have also been reported in patients with no known risk factors. Suspend adefovir in any patient who develops clinical or laboratory findings suggestive of lactic acidosis or pronounced hepatotoxicity (which may include hepatomegaly and steatosis even in the absence of marked transaminase elevations).
    Ado-Trastuzumab emtansine: (Major) Avoid coadministration of ritonavir with ado-trastuzumab emtansine if possible due to the risk of elevated exposure to the cytotoxic component of ado-trastuzumab emtansine, DM1. Delay ado-trastuzumab emtansine treatment until ritonavir has cleared from the circulation (approximately 3 half-lives of ritonavir) when possible. If concomitant use is unavoidable, closely monitor patients for ado-trastuzumab emtansine-related adverse reactions. The cytotoxic component of ado-trastuzumab emtansine, DM1, is metabolized mainly by CYP3A4 and to a lesser extent by CYP3A5; ritonavir is a strong CYP3A4 inhibitor. Formal drug interaction studies with ado-trastuzumab emtansine have not been conducted.
    Afatinib: (Moderate) If the concomitant use of paritaprevir and afatinib is necessary, monitor for afatinib-related adverse reactions. If the original dose of afatinib is not tolerated, consider reducing the daily dose of afatinib by 10 mg; resume the previous dose of afatinib as tolerated after discontinuation of paritaprevir. The manufacturer of afatinib recommends permanent discontinuation of therapy for severe or intolerant adverse drug reactions at a dose of 20 mg per day, but does not address a minimum dose otherwise. Afatinib is a P-glycoprotein (P-gp) substrate and paritaprevir is a P-gp inhibitor; coadministration may increase plasma concentrations of afatinib. Administration with another P-gp inhibitor, given 1 hour before a single dose of afatinib, increased afatinib exposure by 48%; there was no change in afatinib exposure when the P-gp inhibitor was administered at the same time as afatinib or 6 hours later. In healthy subjects, the relative bioavailability for AUC and Cmax of afatinib was 119% and 104%, respectively, when coadministered with the same P-gp inhibitor, and 111% and 105% when the inhibitor was administered 6 hours after afatinib. (Moderate) If the concomitant use of ritonavir and afatinib is necessary, monitor for afatinib-related adverse reactions. If the original dose of afatinib is not tolerated, consider reducing the daily dose of afatinib by 10 mg; resume the previous dose of afatinib as tolerated after discontinuation of ritonavir. The manufacturer of afatinib recommends permanent discontinuation of therapy for severe or intolerant adverse drug reactions at a dose of 20 mg per day, but does not address a minimum dose otherwise. Afatinib is a P-glycoprotein (P-gp) substrate and ritonavir is a P-gp inhibitor; coadministration may increase plasma concentrations of afatinib. Administration with another P-gp inhibitor, given 1 hour before a single dose of afatinib, increased afatinib exposure by 48%; there was no change in afatinib exposure when the P-gp inhibitor was administered at the same time as afatinib or 6 hours later. In healthy subjects, the relative bioavailability for AUC and Cmax of afatinib was 119% and 104%, respectively, when coadministered with the same P-gp inhibitor, and 111% and 105% when the inhibitor was administered 6 hours after afatinib.
    Aldesleukin, IL-2: (Moderate) Concurrent administration of aldesleukin, IL-2 with dasabuvir; ombitasvir; paritaprevir; ritonavir or ombitasvir; paritaprevir; ritonavir may result in increased plasma concentrations of paritaprevir, ritonavir and dasabuvir. Aldesleukin, IL-2 increases IL-6 concentrations, and IL-6 is an inhibitor of the hepatic isoenzyme CYP3A4; paritaprevir, ritonavir and dasabuvir (minor) are substrates of this enzyme. Caution and close monitoring are advised if these drugs are administered together. (Moderate) Concurrent administration of aldesleukin, IL-2 with ritonavir may result in increased plasma concentrations of ritonavir. Aldesleukin, IL-2 increases IL-6 concentrations, and IL-6 is an inhibitor of the hepatic isoenzyme CYP3A4; ritonavir is a substrate of this enzyme. Caution and close monitoring are advised if these drugs are administered together.
    Alfentanil: (Moderate) Alfentanil is metabolized by the hepatic isoenzyme CYP3A4. Drugs that inhibit this enzyme, such as protease inhibitors, may alter responses to alfentanil. A dose reduction of one or both drugs may be warranted. Monitor closely for oversedation and respiratory depression.
    Alfuzosin: (Severe) Coadministration of alfuzosin with protease inhibitors is contraindicated due to potential hypotension. Alfuzosin is a CYP3A4 substrate and protease inhibitors are strong CYP3A4 inhibitors.
    Aliskiren: (Moderate) The plasma concentrations of aliskiren may be elevated when administered concurrently with ritonavir. Clinical monitoring for adverse effects, such as decreased blood pressure, is recommended during coadministration. Ritonavir is an inhibitor of CYP3A4 and P-glycoprotein (P-gp). Aliskiren is a substrate of both CYP3A4 and P-gp.
    Aliskiren; Amlodipine: (Moderate) Amlodipine is a CYP3A4 substrate. Theoretically, CYP3A4 inhibitors, such as anti-retroviral protease inhibitors, may increase the plasma concentration of amlodipine via CYP3A4 inhibition; this effect might lead to hypotension in some individuals. Caution should be used when anti-retroviral protease inhibitors are coadministered with amlodipine; therapeutic response should be monitored. Ritonavir also prolongs the PR interval in some patients; however, the impact on the PR interval of coadministration of ritonavir with other drugs that prolong the PR interval (including calcium channel blockers) has not been evaluated. If coadministration of these drugs is warranted, do so with caution and careful monitoring. Decreased calcium-channel blocker doses may be warranted. (Moderate) The plasma concentrations of aliskiren may be elevated when administered concurrently with ritonavir. Clinical monitoring for adverse effects, such as decreased blood pressure, is recommended during coadministration. Ritonavir is an inhibitor of CYP3A4 and P-glycoprotein (P-gp). Aliskiren is a substrate of both CYP3A4 and P-gp.
    Aliskiren; Amlodipine; Hydrochlorothiazide, HCTZ: (Moderate) Amlodipine is a CYP3A4 substrate. Theoretically, CYP3A4 inhibitors, such as anti-retroviral protease inhibitors, may increase the plasma concentration of amlodipine via CYP3A4 inhibition; this effect might lead to hypotension in some individuals. Caution should be used when anti-retroviral protease inhibitors are coadministered with amlodipine; therapeutic response should be monitored. Ritonavir also prolongs the PR interval in some patients; however, the impact on the PR interval of coadministration of ritonavir with other drugs that prolong the PR interval (including calcium channel blockers) has not been evaluated. If coadministration of these drugs is warranted, do so with caution and careful monitoring. Decreased calcium-channel blocker doses may be warranted. (Moderate) The plasma concentrations of aliskiren may be elevated when administered concurrently with ritonavir. Clinical monitoring for adverse effects, such as decreased blood pressure, is recommended during coadministration. Ritonavir is an inhibitor of CYP3A4 and P-glycoprotein (P-gp). Aliskiren is a substrate of both CYP3A4 and P-gp.
    Aliskiren; Hydrochlorothiazide, HCTZ: (Moderate) The plasma concentrations of aliskiren may be elevated when administered concurrently with ritonavir. Clinical monitoring for adverse effects, such as decreased blood pressure, is recommended during coadministration. Ritonavir is an inhibitor of CYP3A4 and P-glycoprotein (P-gp). Aliskiren is a substrate of both CYP3A4 and P-gp.
    Aliskiren; Valsartan: (Moderate) Coadministration of valsartan and regimens containing paritaprevir may result in elevated valsartan plasma concentrations. A valsartan dose reduction, and close monitoring for adverse events (i.e., hypotension and worsening renal function) are advised during coadministration. If adverse events are observed, consider further reductions in valsartan dose or an alternative to the angiotensin receptor blocker. Valsartan is a substrate of the organic anion transporting polypeptides (OATP) and paritaprevir is an OATP1B1 and OATP1B3 inhibitor. (Moderate) The plasma concentrations of aliskiren may be elevated when administered concurrently with ritonavir. Clinical monitoring for adverse effects, such as decreased blood pressure, is recommended during coadministration. Ritonavir is an inhibitor of CYP3A4 and P-glycoprotein (P-gp). Aliskiren is a substrate of both CYP3A4 and P-gp. (Minor) Valsartan is a substrate of the hepatic efflux transporter MRP2 and ritonavir is an inhibitor of MRP2. Coadministration may increase systemic exposure to valsartan. Patients should be monitored for adverse effects of valsartan during coadministration.
    Almotriptan: (Major) Ombitasvir; paritaprevir; ritonavir may increase the systemic exposure of almotriptan. If coadministered, the recommended starting dose of almotriptan is 6.25 mg; do not exceed 12.5 mg within a 24-hour period. Avoid coadministration in patients with renal or hepatic impairment. Almotriptan is a CYP3A4 substrate and ritonavir is a potent CYP3A4 inhibitor. In a drug interaction study, coadministration of almotriptan and ketoconazole, another potent CYP3A4 inhibitor, resulted in an approximately 60% increase in almotriptan exposure. (Major) Ritonavir may increase the systemic exposure of almotriptan. If coadministered, the recommended starting dose of almotriptan is 6.25 mg; do not exceed 12.5 mg within a 24-hour period. Avoid coadministration in patients with renal or hepatic impairment. Almotriptan is a CYP3A4 substrate and ritonavir is a potent CYP3A4 inhibitor. In a drug interaction study, coadministration of almotriptan and ketoconazole, another potent CYP3A4 inhibitor, resulted in an approximately 60% increase in almotriptan exposure.
    Alogliptin: (Moderate) New onset diabetes mellitus, exacerbation of diabetes mellitus, and hyperglycemia due to insulin resistance have been reported with use of anti-retroviral protease inhibitors. A possible mechanism is impairment of beta-cell function. Onset averaged approximately 63 days after initiating protease inhibitor therapy, but has occurred as early as 4 days after beginning therapy. Diabetic ketoacidosis has occurred in some patients including patients who were not diabetic prior to protease inhibitor treatment. Patients on antidiabetic therapy should be closely monitored for changes in glycemic control, specifically hyperglycemia, if protease inhibitor therapy is initiated.
    Alogliptin; Metformin: (Major) While no dosage adjustment of metformin is recommended in patients with normal hepatic or renal function, careful patient monitoring and dose adjustment of metformin and/or the potentially interfering drug is recommended with concurrent use. Monitor for signs of onset of lactic acidosis such as respiratory distress, somnolence, and non-specific abdominal distress or worsening renal function. Do not use metformin with paritaprevir in patients with renal insufficiency or hepatic impairment. Drugs that interfere with common renal tubular transport systems involved in the renal elimination of metformin could increase systemic exposure to metformin and may increase the risk for lactic acidosis. Paritaprevir is an inhibitor of the organic anion transporters OATP1B1 and OATP1B3. While initial drug-drug interaction studies of paritaprevir-containing hepatitis treatments have not noted an effect on metformin concentrations, more study is needed. (Moderate) New onset diabetes mellitus, exacerbation of diabetes mellitus, and hyperglycemia due to insulin resistance have been reported with use of anti-retroviral protease inhibitors. A possible mechanism is impairment of beta-cell function. Onset averaged approximately 63 days after initiating protease inhibitor therapy, but has occurred as early as 4 days after beginning therapy. Diabetic ketoacidosis has occurred in some patients including patients who were not diabetic prior to protease inhibitor treatment. Patients on antidiabetic therapy should be closely monitored for changes in glycemic control, specifically hyperglycemia, if protease inhibitor therapy is initiated. (Moderate) New onset diabetes mellitus, exacerbation of diabetes mellitus, and hyperglycemia due to insulin resistance have been reported with use of anti-retroviral protease inhibitors. Another possible mechanism is impairment of beta-cell function. Onset averaged approximately 63 days after initiating protease inhibitor therapy, but has occurred as early as 4 days after beginning therapy. Diabetic ketoacidosis has occurred in some patients including patients who were not diabetic prior to protease inhibitor treatment. Patients taking antidiabetic therapy should be closely monitored for changes in glycemic control, specifically hyperglycemia, if protease inhibitor therapy is initiated.
    Alogliptin; Pioglitazone: (Moderate) New onset diabetes mellitus, exacerbation of diabetes mellitus, and hyperglycemia due to insulin resistance have been reported with use of anti-retroviral protease inhibitors. A possible mechanism is impairment of beta-cell function. Onset averaged approximately 63 days after initiating protease inhibitor therapy, but has occurred as early as 4 days after beginning therapy. Diabetic ketoacidosis has occurred in some patients including patients who were not diabetic prior to protease inhibitor treatment. Patients on antidiabetic therapy should be closely monitored for changes in glycemic control, specifically hyperglycemia, if protease inhibitor therapy is initiated.
    Alosetron: (Major) Concurrent administration of alosetron with ritonavir may alter alosetron plasma concentrations; however, the precise effect is undefined. Alosetron is metabolized by the hepatic isoenzymes CYP3A4, CYP2C9, and CYP1A2; ritonavir is an inhibitor of CYP3A4 and an inducer of CYP1A2 and possibly CYP2C9. Caution and close monitoring are advised if these drugs are administered together.
    Alpelisib: (Major) Avoid coadministration of alpelisib with paritaprevir due to increased exposure to alpelisib and the risk of alpelisib-related toxicity. If concomitant use is unavoidable, closely monitor for alpelisib-related adverse reactions. Alpelisib is a BCRP substrate and paritaprevir is a BCRP inhibitor.
    Alpha-glucosidase Inhibitors: (Moderate) New onset diabetes mellitus, exacerbation of diabetes mellitus, and hyperglycemia due to insulin resistance have been reported with use of anti-retroviral protease inhibitors.
    Alprazolam: (Major) Coadministration of alprazolam and ritonavir is not recommended. If coadministration cannot be avoided, a dosage reduction of alprazolam should be considered. Ritonavir is a potent CYP3A4 inhibitor. The initial step in alprazolam metabolism is hydroxylation catalyzed by cytochrome CYP3A. Drugs that inhibit this metabolic pathway may profoundly decrease alprazolam clearance, resulting in increased potential for serious alprazolam-related adverse events, such as respiratory depression and prolonged sedation. Consequently, alprazolam should be avoided in patients receiving very potent inhibitors of CYP3A isoenzymes.
    Amiodarone: (Major) Coadministration of HIV treatment doses of ritonavir and amiodarone is contraindicated due to the potential for serious or life-threatening reactions, such as cardiac arrhythmias. Cautious consideration may be given to administering amiodarone with boosting doses of ritonavir. Ritonavir is an inhibitor of CYP3A4 and increased plasma concentrations of drugs extensively metabolized by this enzyme, such as amiodarone, should be expected with concurrent use.
    Amitriptyline: (Major) Concurrent administration of amitriptyline with dasabuvir; ombitasvir; paritaprevir; ritonavir or ombitasvir; paritaprevir; ritonavir may result in elevated amitriptyline plasma concentrations; however, the clinical implications of this interaction have not been clearly defined. Amitriptyline is a substrate of the hepatic isoenzymes CYP3A4 and CYP2D6 and uridine glucuronyltransferase (UGT). Ritonavir inhibits CYP3A4 and CYP2D6, while dasabuvir, ombitasvir and paritaprevir are UGT1A1 inhibitors. Hepatic isoenzymes CYP1A2, CYP2C9, and CYP2C19 also contribute to amitriptyline's metabolism, and these isoenzymes do not appear to be inhibited by the 4-drug regimen. Caution and close monitoring are advised if these drugs are administered together. (Moderate) A dose reduction of the tricyclic antidepressant (TCA) may be necessary when coadministered with ritonavir. Concurrent use may result in elevated TCA plasma concentrations.
    Amitriptyline; Chlordiazepoxide: (Major) Concurrent administration of amitriptyline with dasabuvir; ombitasvir; paritaprevir; ritonavir or ombitasvir; paritaprevir; ritonavir may result in elevated amitriptyline plasma concentrations; however, the clinical implications of this interaction have not been clearly defined. Amitriptyline is a substrate of the hepatic isoenzymes CYP3A4 and CYP2D6 and uridine glucuronyltransferase (UGT). Ritonavir inhibits CYP3A4 and CYP2D6, while dasabuvir, ombitasvir and paritaprevir are UGT1A1 inhibitors. Hepatic isoenzymes CYP1A2, CYP2C9, and CYP2C19 also contribute to amitriptyline's metabolism, and these isoenzymes do not appear to be inhibited by the 4-drug regimen. Caution and close monitoring are advised if these drugs are administered together. (Major) CYP3A4 inhibitors, such as protease inhibitors, may reduce the metabolism of chlordiazepoxide and increase the potential for benzodiazepine toxicity. A decrease in the chlordiazepoxide dose may be needed. (Moderate) A dose reduction of the tricyclic antidepressant (TCA) may be necessary when coadministered with ritonavir. Concurrent use may result in elevated TCA plasma concentrations.
    Amlodipine: (Moderate) Amlodipine is a CYP3A4 substrate. Theoretically, CYP3A4 inhibitors, such as anti-retroviral protease inhibitors, may increase the plasma concentration of amlodipine via CYP3A4 inhibition; this effect might lead to hypotension in some individuals. Caution should be used when anti-retroviral protease inhibitors are coadministered with amlodipine; therapeutic response should be monitored. Ritonavir also prolongs the PR interval in some patients; however, the impact on the PR interval of coadministration of ritonavir with other drugs that prolong the PR interval (including calcium channel blockers) has not been evaluated. If coadministration of these drugs is warranted, do so with caution and careful monitoring. Decreased calcium-channel blocker doses may be warranted.
    Amlodipine; Atorvastatin: (Severe) Concomitant use of ombitasvir; paritaprevir; ritonavir with atorvastatin is contraindicated due to the potential for severe adverse reactions, including myopathy and rhabdomyolysis. Coadministration may result in elevated atorvastatin systemic concentrations. Atorvastatin is a substrate of the hepatic isoenzyme CYP3A4; ritonavir is a potent inhibitor of this isoenzyme. (Major) Use caution and the lowest atorvastatin dose necessary if atorvastatin must be coadministered with ritonavir. The risk of developing myopathy/rhabdomyolysis increases when atorvastatin is used concomitantly with ritonavir. Monitor patients for any signs or symptoms of muscle pain, weakness, or tenderness especially in the initial months of therapy and any time the dosage of either drug is titrated upward. Protease inhibitors inhibit the CYP3A4 metabolism of atorvastatin. The serious risk of myopathy or rhabdomyolysis should be weighed carefully against the benefits of combined 'statin' and lopinavir; ritonavir therapy; there is no assurance that periodic monitoring of CK will prevent the occurrence of severe myopathy and renal damage. (Moderate) Amlodipine is a CYP3A4 substrate. Theoretically, CYP3A4 inhibitors, such as anti-retroviral protease inhibitors, may increase the plasma concentration of amlodipine via CYP3A4 inhibition; this effect might lead to hypotension in some individuals. Caution should be used when anti-retroviral protease inhibitors are coadministered with amlodipine; therapeutic response should be monitored. Ritonavir also prolongs the PR interval in some patients; however, the impact on the PR interval of coadministration of ritonavir with other drugs that prolong the PR interval (including calcium channel blockers) has not been evaluated. If coadministration of these drugs is warranted, do so with caution and careful monitoring. Decreased calcium-channel blocker doses may be warranted.
    Amlodipine; Benazepril: (Moderate) Amlodipine is a CYP3A4 substrate. Theoretically, CYP3A4 inhibitors, such as anti-retroviral protease inhibitors, may increase the plasma concentration of amlodipine via CYP3A4 inhibition; this effect might lead to hypotension in some individuals. Caution should be used when anti-retroviral protease inhibitors are coadministered with amlodipine; therapeutic response should be monitored. Ritonavir also prolongs the PR interval in some patients; however, the impact on the PR interval of coadministration of ritonavir with other drugs that prolong the PR interval (including calcium channel blockers) has not been evaluated. If coadministration of these drugs is warranted, do so with caution and careful monitoring. Decreased calcium-channel blocker doses may be warranted.
    Amlodipine; Celecoxib: (Moderate) Amlodipine is a CYP3A4 substrate. Theoretically, CYP3A4 inhibitors, such as anti-retroviral protease inhibitors, may increase the plasma concentration of amlodipine via CYP3A4 inhibition; this effect might lead to hypotension in some individuals. Caution should be used when anti-retroviral protease inhibitors are coadministered with amlodipine; therapeutic response should be monitored. Ritonavir also prolongs the PR interval in some patients; however, the impact on the PR interval of coadministration of ritonavir with other drugs that prolong the PR interval (including calcium channel blockers) has not been evaluated. If coadministration of these drugs is warranted, do so with caution and careful monitoring. Decreased calcium-channel blocker doses may be warranted.
    Amlodipine; Hydrochlorothiazide, HCTZ; Olmesartan: (Moderate) Amlodipine is a CYP3A4 substrate. Theoretically, CYP3A4 inhibitors, such as anti-retroviral protease inhibitors, may increase the plasma concentration of amlodipine via CYP3A4 inhibition; this effect might lead to hypotension in some individuals. Caution should be used when anti-retroviral protease inhibitors are coadministered with amlodipine; therapeutic response should be monitored. Ritonavir also prolongs the PR interval in some patients; however, the impact on the PR interval of coadministration of ritonavir with other drugs that prolong the PR interval (including calcium channel blockers) has not been evaluated. If coadministration of these drugs is warranted, do so with caution and careful monitoring. Decreased calcium-channel blocker doses may be warranted.
    Amlodipine; Hydrochlorothiazide, HCTZ; Valsartan: (Moderate) Amlodipine is a CYP3A4 substrate. Theoretically, CYP3A4 inhibitors, such as anti-retroviral protease inhibitors, may increase the plasma concentration of amlodipine via CYP3A4 inhibition; this effect might lead to hypotension in some individuals. Caution should be used when anti-retroviral protease inhibitors are coadministered with amlodipine; therapeutic response should be monitored. Ritonavir also prolongs the PR interval in some patients; however, the impact on the PR interval of coadministration of ritonavir with other drugs that prolong the PR interval (including calcium channel blockers) has not been evaluated. If coadministration of these drugs is warranted, do so with caution and careful monitoring. Decreased calcium-channel blocker doses may be warranted. (Moderate) Coadministration of valsartan and regimens containing paritaprevir may result in elevated valsartan plasma concentrations. A valsartan dose reduction, and close monitoring for adverse events (i.e., hypotension and worsening renal function) are advised during coadministration. If adverse events are observed, consider further reductions in valsartan dose or an alternative to the angiotensin receptor blocker. Valsartan is a substrate of the organic anion transporting polypeptides (OATP) and paritaprevir is an OATP1B1 and OATP1B3 inhibitor. (Minor) Valsartan is a substrate of the hepatic efflux transporter MRP2 and ritonavir is an inhibitor of MRP2. Coadministration may increase systemic exposure to valsartan. Patients should be monitored for adverse effects of valsartan during coadministration.
    Amlodipine; Olmesartan: (Moderate) Amlodipine is a CYP3A4 substrate. Theoretically, CYP3A4 inhibitors, such as anti-retroviral protease inhibitors, may increase the plasma concentration of amlodipine via CYP3A4 inhibition; this effect might lead to hypotension in some individuals. Caution should be used when anti-retroviral protease inhibitors are coadministered with amlodipine; therapeutic response should be monitored. Ritonavir also prolongs the PR interval in some patients; however, the impact on the PR interval of coadministration of ritonavir with other drugs that prolong the PR interval (including calcium channel blockers) has not been evaluated. If coadministration of these drugs is warranted, do so with caution and careful monitoring. Decreased calcium-channel blocker doses may be warranted.
    Amlodipine; Telmisartan: (Moderate) Amlodipine is a CYP3A4 substrate. Theoretically, CYP3A4 inhibitors, such as anti-retroviral protease inhibitors, may increase the plasma concentration of amlodipine via CYP3A4 inhibition; this effect might lead to hypotension in some individuals. Caution should be used when anti-retroviral protease inhibitors are coadministered with amlodipine; therapeutic response should be monitored. Ritonavir also prolongs the PR interval in some patients; however, the impact on the PR interval of coadministration of ritonavir with other drugs that prolong the PR interval (including calcium channel blockers) has not been evaluated. If coadministration of these drugs is warranted, do so with caution and careful monitoring. Decreased calcium-channel blocker doses may be warranted.
    Amlodipine; Valsartan: (Moderate) Amlodipine is a CYP3A4 substrate. Theoretically, CYP3A4 inhibitors, such as anti-retroviral protease inhibitors, may increase the plasma concentration of amlodipine via CYP3A4 inhibition; this effect might lead to hypotension in some individuals. Caution should be used when anti-retroviral protease inhibitors are coadministered with amlodipine; therapeutic response should be monitored. Ritonavir also prolongs the PR interval in some patients; however, the impact on the PR interval of coadministration of ritonavir with other drugs that prolong the PR interval (including calcium channel blockers) has not been evaluated. If coadministration of these drugs is warranted, do so with caution and careful monitoring. Decreased calcium-channel blocker doses may be warranted. (Moderate) Coadministration of valsartan and regimens containing paritaprevir may result in elevated valsartan plasma concentrations. A valsartan dose reduction, and close monitoring for adverse events (i.e., hypotension and worsening renal function) are advised during coadministration. If adverse events are observed, consider further reductions in valsartan dose or an alternative to the angiotensin receptor blocker. Valsartan is a substrate of the organic anion transporting polypeptides (OATP) and paritaprevir is an OATP1B1 and OATP1B3 inhibitor. (Minor) Valsartan is a substrate of the hepatic efflux transporter MRP2 and ritonavir is an inhibitor of MRP2. Coadministration may increase systemic exposure to valsartan. Patients should be monitored for adverse effects of valsartan during coadministration.
    Amobarbital: (Major) Concurrent use of ritonavir with phenobarbital or other barbiturates should be done cautiously. Increased doses of anticonvulsants may be required due metabolism induction by ritonavir. However, since these anticonvulsants are hepatic enzyme inducing drugs, increased metabolism of protease inhibitors may occur, leading to decreased antiretroviral efficacy. Close monitoring of drug concentrations and/or therapeutic and adverse effects is required.
    Amoxapine: (Major) Ritonavir potently inhibits CYP2D6, and may inhibit the metabolism of amoxapine. Since the magnitude of the interaction with the amoxapine is difficult to predict but may be significant, monitor patients receiving ritonavir and amoxapine concurrently closely. Adjust the dosage of the coadministered drug based on therapeutic response. Amoxapine serum concentration monitoring may be useful to guide adjustments and prevent toxicity.
    Amoxicillin; Clarithromycin; Lansoprazole: (Major) Because the exposure to 14-OH clarithromycin is significantly decreased by ritonavir, consider alternative antibiotic therapy for indications other than Mycobacterium avium. Clarithromycin doses above 1000 mg should not be administered with ritonavir. If coadministration cannot be avoided, clarithromycin dosage reductions are recommended in patients with renal impairment (CrCl 30 to 60 mL/minute, decrease clarithromycin by 50%; CrCl less than 30 mL/minute, decrease clarithromycin by 75%). Concomitant administration of ritonavir and clarithromycin resulted in a 77% increase in clarithromycin exposure and a 100% decrease in 14-OH clarithromycin exposure. The microbiological activities of clarithromycin and 14-OH-clarithromycin are different for different bacteria. (Moderate) Caution is advised when administering clarithromycin concurrently with ombitasvir. Use of these drugs together may result in elevated concentrations of ombitasvir. Clarithromycin is an inhibitor of P-glycoprotein (P-gp). Ombitasvir is a substrate of P-gp. (Moderate) Caution is advised when administering clarithromycin concurrently with paritaprevir. Use of these drugs together may result in elevated concentrations of paritaprevir. Clarithromycin is an inhibitor of CYP3A4 and P-glycoprotein (P-gp). Paritaprevir is a substrate of CYP3A4 and P-gp. (Moderate) Increased exposure to lansoprazole may occur during concurrent administration of ritonavir. Although dosage adjustment of lansoprazole is not normally required, dosage reduction may be considered in patients receiving higher lansoprazole doses (e.g., those with Zollinger-Ellison syndrome). Ritonavir is a strong CYP3A4 inhibitor. Lansoprazole is a CYP2C19 and CYP3A4 substrate. Coadministration of a dual CYP2C19/strong CYP3A4 inhibitor increased the lansoprazole AUC by an average of 4-times.
    Amoxicillin; Clarithromycin; Omeprazole: (Major) Because the exposure to 14-OH clarithromycin is significantly decreased by ritonavir, consider alternative antibiotic therapy for indications other than Mycobacterium avium. Clarithromycin doses above 1000 mg should not be administered with ritonavir. If coadministration cannot be avoided, clarithromycin dosage reductions are recommended in patients with renal impairment (CrCl 30 to 60 mL/minute, decrease clarithromycin by 50%; CrCl less than 30 mL/minute, decrease clarithromycin by 75%). Concomitant administration of ritonavir and clarithromycin resulted in a 77% increase in clarithromycin exposure and a 100% decrease in 14-OH clarithromycin exposure. The microbiological activities of clarithromycin and 14-OH-clarithromycin are different for different bacteria. (Moderate) Caution is advised when administering clarithromycin concurrently with ombitasvir. Use of these drugs together may result in elevated concentrations of ombitasvir. Clarithromycin is an inhibitor of P-glycoprotein (P-gp). Ombitasvir is a substrate of P-gp. (Moderate) Caution is advised when administering clarithromycin concurrently with paritaprevir. Use of these drugs together may result in elevated concentrations of paritaprevir. Clarithromycin is an inhibitor of CYP3A4 and P-glycoprotein (P-gp). Paritaprevir is a substrate of CYP3A4 and P-gp. (Moderate) Dosage adjustments of omeprazole may be required during concomitant administration with dasabuvir; ombitasvir; paritaprevir; ritonavir. Use of these drugs together results in decreased omeprazole serum concentrations. Monitor for decreasing efficacy and consider increasing the omeprazole dose if needed; however, adult doses should be limited to no more than 40 mg/day. The dose should be re-adjusted after completion of the 4-drug hepatitis C treatment regimen. (Moderate) Increased exposure to omeprazole may occur during concurrent administration of ritonavir. Although dosage adjustment of omeprazole is not normally required, dosage reduction may be considered in patients receiving higher omeprazole doses (e.g., those with Zollinger-Ellison syndrome). Ritonavir is a strong CYP3A4 inhibitor. Omeprazole is a CYP2C19 and CYP3A4 substrate. Coadministration of a dual CYP2C19/strong CYP3A4 inhibitor increased the omeprazole AUC by an average of 4-times.
    Amphetamine: (Moderate) Warn patients that the risk of amphetamine toxicity may be increased during concurrent use of ritonavir, a strong CYP2D6 inhibitor. Amphetamines are partially metabolized by CYP2D6 and have serotonergic properties; inhibition of amphetamine metabolism may increase the risk of serotonin syndrome or other toxicity. If serotonin syndrome occurs, both the amphetamine and CYP2D6 inhibitor should be discontinued and appropriate medical treatment should be implemented.
    Amphetamine; Dextroamphetamine: (Moderate) Warn patients that the risk of amphetamine toxicity may be increased during concurrent use of ritonavir, a strong CYP2D6 inhibitor. Amphetamines are partially metabolized by CYP2D6 and have serotonergic properties; inhibition of amphetamine metabolism may increase the risk of serotonin syndrome or other toxicity. If serotonin syndrome occurs, both the amphetamine and CYP2D6 inhibitor should be discontinued and appropriate medical treatment should be implemented.
    Amphetamines: (Moderate) Warn patients that the risk of amphetamine toxicity may be increased during concurrent use of ritonavir, a strong CYP2D6 inhibitor. Amphetamines are partially metabolized by CYP2D6 and have serotonergic properties; inhibition of amphetamine metabolism may increase the risk of serotonin syndrome or other toxicity. If serotonin syndrome occurs, both the amphetamine and CYP2D6 inhibitor should be discontinued and appropriate medical treatment should be implemented.
    Apalutamide: (Severe) Coadministration of paritaprevir with apalutamide is contraindicated due to the potential for decreased paritaprevir concentrations and the potential development of viral resistance. Paritaprevir is metabolized by CYP3A4 and apalutamide is a strong CYP3A4 inducer. Coadministration with another strong CYP3A4 inducer decreased paritaprevir exposure by 70%. (Severe) Coadministration of ritonavir with apalutamide is contraindicated as there is a potential for decreased ritonavir concentrations which may lead to a reduction of antiretroviral efficacy and the potential development of viral resistance; exposure to apalutamide may also increase. Ritonavir is a CYP3A4 substrate and strong inhibitor. Apalutamide is a CYP3A4 substrate and strong inducer.
    Apixaban: (Major) Concurrent administration of apixaban with dasabuvir; ombitasvir; paritaprevir; ritonavir or ombitasvir; paritaprevir; ritonavir requires a dosage adjustment for apixaban. For patients receiving more than 2.5 mg PO twice daily of apixaban, reduce the apixaban dosage by 50%. For patients receiving apixaban 2.5 mg PO twice daily, avoid coadministration with dasabuvir; ombitasvir; paritaprevir; ritonavir or ombitasvir; paritaprevir; ritonavir. Apixaban is a substrate of both CYP3A4 and P-glycoprotein (P-gp); ritonavir inhibits both CYP3A4 and P-gp and paritaprevir inhibits P-gp. Coadministration of these agents increases apixaban plasma concentrations and risk of adverse events such as bleeding. (Major) Reduce the apixaban dose by 50% when coadministered with drugs that are both strong inhibitors of CYP3A4 and P-gp, such as ritonavir. If patients are already receiving the reduced dose of 2.5 mg twice daily, avoid concomitant administration of apixaban and ritonavir. Concomitant administration of ritonavir and apixaban results in increased exposure to apixaban and an increase in the risk of bleeding.
    Aprepitant, Fosaprepitant: (Major) Avoid the concomitant use of ritonavir with aprepitant, fosaprepitant due to substantially increased exposure of aprepitant; after administration, fosaprepitant is rapidly converted to aprepitant and shares many of the same drug interactions. Increased ritonavir exposure may also occur. If coadministration cannot be avoided, use caution and monitor for an increase in ritonavir- and aprepitant-related adverse effects for several days after administration of a multi-day aprepitant regimen. Ritonavir is a strong CYP3A4 inhibitor and aprepitant is a CYP3A4 substrate. Coadministration with another strong CYP3A4 inhibitor increased the AUC of aprepitant by approximately 5-fold, and the mean terminal half-life by approximately 3-fold. Ritonavir is also a is also a CYP3A4 substrate. Aprepitant, when administered as a 3-day oral regimen (125 mg/80 mg/80 mg), is a moderate CYP3A4 inhibitor. When administered as a single oral or single intravenous dose, the inhibitory effect of aprepitant on CYP3A4 is weak and does not result in a clinically significant increase in the AUC of a sensitive substrate. (Moderate) Avoid the concomitant use of ombitasvir; paritaprevir; ritonavir with aprepitant due to substantially increased exposure of aprepitant; increased paritaprevir and ritonavir exposure may also occur. If coadministration cannot be avoided, use caution and monitor for an increase in paritaprevir-, ritonavir-, and aprepitant-related adverse effects for several days after administration of a multi-day aprepitant regimen. After administration, fosaprepitant is rapidly converted to aprepitant and shares the same drug interactions. Ritonavir is a strong CYP3A4 inhibitor and aprepitant is a CYP3A4 substrate. Coadministration of a single oral dose of aprepitant (125 mg) on day 5 of a 10-day ketoconazole regimen (strong CYP3A4 inhibitor) increased the aprepitant AUC approximately 5-fold, and increased the mean terminal half-life by approximately 3-fold. Paritaprevir and ritonavir are also CYP3A4 substrates. Aprepitant, when administered as a 3-day oral regimen (125 mg/80 mg/80 mg), is a moderate CYP3A4 inhibitor and inducer; substitution of fosaprepitant 115 mg IV on day 1 of the 3-day regimen may lessen the inhibitory effects of CYP3A4. The AUC of a single dose of another CYP3A4 substrate, midazolam, increased by 2.3-fold and 3.3-fold on days 1 and 5, respectively, when coadministered with a 5-day oral aprepitant regimen. After a 3-day oral aprepitant regimen, the AUC of midazolam increased by 25% on day 4, and decreased by 19% and 4% on days 8 and 15, respectively, when given on days 1, 4, 8, and 15. As a single 40-mg oral dose, the inhibitory effect of aprepitant on CYP3A4 is weak, with the AUC of midazolam increased by 1.2-fold; the midazolam AUC increased by 1.5-fold after a single 125-mg dose of oral aprepitant. After single doses of IV fosaprepitant, the midazolam AUC increased by 1.8-fold (150 mg) and 1.6-fold (100 mg); less than a 2-fold increase in the midazolam AUC is not considered clinically important.
    Arformoterol: (Moderate) The use of ritonavir could result in QT prolongation. Drugs with a possible risk for QT prolongation and TdP that should be used cautiously and with close monitoring with ritonavir, include beta-agonists.
    Aripiprazole: (Major) Because aripiprazole is metabolized by CYP3A4 and CYP2D6, the manufacturer recommends that the oral aripiprazole dose be reduced to one-quarter (25%) of the usual dose in patients receiving inhibitors of both CYP3A4 and CYP2D6 such as ritonavir. Patients classified as CYP2D6 poor metabolizers (PMs) who are receiving a strong CYP3A4 inhibitor should have their oral aripiprazole dose reduced to one-quarter (25%) of the usual dose with subsequent adjustments based upon clinical response. Adults receiving a combination of a CYP3A4 and CYP2D6 inhibitor for more than 14 days should have their Abilify Maintena dose reduced from 400 mg/month to 200 mg/month or from 300 mg/month to 160 mg/month, respectively. Adults receiving Abilify Maintena who are PMs and receiving a strong CYP3A4 inhibitor, such as ritonavir, should have a dose reduction to 200 mg/month IM. In adults receiving Aristada, the Aristada dose should be reduced to the next lower strength during use of a strong CYP3A4 inhibitor for more than 14 days. For patients receiving 882 mg of Aristada every 6 weeks or 1064 mg every 2 months, the next lower strength should be 441 mg administered every 4 weeks. No dosage adjustment is necessary in patients taking 441 mg IM of Aristada, if tolerated. Adults receiving Aristada who are PMs of CYP2D6 and receiving a strong CYP3A4 inhibitor for more than 14 days should have their dose reduced from 662 mg, 882 mg, or 1064 mg to 441 mg IM; no dose adjustment is needed in patients receiving 441 mg of Aristada, if tolerated. In adults receiving Aristada 662 mg, 882 mg, or 1064 mg, combined use of a strong CYP2D6 inhibitor and a strong CYP3A4 inhibitor for more than 14 days should be avoided; no dose adjustment is needed in patients taking 441 mg, if tolerated. Avoid concurrent use of Aristada Initio and strong CYP3A4 inhibitors because the dose of Aristada Initio cannot be modified.
    Armodafinil: (Severe) Concurrent administration of armodafinil with dasabuvir; ombitasvir; paritaprevir; ritonavir or ombitasvir; paritaprevir; ritonavir is contraindicated. Taking these drugs together could result in decreased plasma concentrations of paritaprevir, ritonavir, and dasabuvir, which may affect antiviral efficacy. Armodafinil is an inducer of the hepatic isoenzyme CYP3A4; paritaprevir, ritonavir and dasabuvir (minor) are substrates of this enzyme. (Major) Coadministration of ritonavir with armodafinil may result in elevated armodafinil concentrations and decreased ritonavir concentrations. Decreased antiretroviral concentrations may lead to a reduction of antiretroviral efficacy and the potential development of viral resistance. Armodafinil is a substrate and inducer of CYP3A4, and a P-glycoprotein (P-gp) substrate. Ritonavir is a substrate of CYP3A4 and an inhibitor of P-gp. Ritonavir is also a potent inhibitor of CYP3A4.
    Artemether; Lumefantrine: (Major) Ritonavir is a substrate, potent inhibitor, and inducer of the CYP3A4 isoenzyme, depending on the activity of the coadministered drug. Both components of artemether; lumefantrine are substrates of the CYP3A4 isoenzyme; therefore, coadministration may lead to increased or decreased artemether; lumefantrine concentrations. Concomitant use warrants caution due to the potential for increased side effects, including increased potentiation of QT prolongation due to increased drug concentrations, or loss of antimalarial activity depending on the artemether; lumefantrine concentrations. Consider ECG monitoring if ritonavir must be used with or after artemether; lumefantrine treatment. (Major) Ritonavir is a substrate, potent inhibitor, and inducer of the CYP3A4 isoenzyme, depending on the activity of the coadministered drug. Both components of artemether; lumefantrine are substrates of the CYP3A4 isoenzyme; therefore, coadministration may lead to increased or decreased artemether; lumefantrine concentrations. Concomitant use warrants caution due to the potential for increased side effects, including increased potentiation of QT prolongation due to increased drug concentrations, or loss of antimalarial activity depending on the artemether; lumefantrine concentrations. Consider ECG monitoring if ritonavir must be used with or after artemether; lumefantrine treatment.
    Artesunate: (Moderate) Monitor for a decre