Nevirapine

Nevirapine is principally metabolized by the liver via the cytochrome P450 isoenzymes, 3A and 2B6. Nevirapine is known to be an inducer of these enzymes. As a result, drugs that are metabolized by these enzyme systems may have lower than expected plasma levels when co-administered with nevirapine. The specific pharmacokinetic changes that occur with co-administration of nevirapine and other drugs are listed in Clinical Pharmacology , Table 5. Clinical comments about possible dosage modifications based on established drug interactions are listed in Table 4.

The data in Tables 4 and 5 are based on the results of drug interaction trials conducted in HIV-1 seropositive subjects unless otherwise indicated. In addition to established drug interactions, there may be potential pharmacokinetic interactions between nevirapine and other drug classes that are metabolized by the cytochrome P450 system. These potential drug interactions are also listed in Table 4. Although specific drug interaction trials in HIV-1 seropositive subjects have not been conducted for some classes of drugs listed in Table 4, additional clinical monitoring may be warranted when co-administering these drugs.

The in vitro interaction between nevirapine and the antithrombotic agent warfarin is complex. As a result, when giving these drugs concomitantly, plasma warfarin levels may change with the potential for increases in coagulation time. When warfarin is co-administered with nevirapine, anticoagulation levels should be monitored frequently. Table 4 Established and Potential Drug Interactions: Use with Caution, Alteration in Dose or Regimen May Be Needed Due to Drug Interaction Established Drug Interactions: See Clinical Pharmacology (12.3) , Table 5 for Magnitude of Interaction.

Drug Name Effect on Concentration of Nevirapine or Concomitant Drug Clinical Comment HIV Antiviral Agents: Protease Inhibitors (PIs) Atazanavir/Ritonavir The interaction between nevirapine and the drug was evaluated in a clinical study. All other drug interactions shown are predicted. ↓ Atazanavir ↑ Nevirapine Do not co-administer nevirapine with atazanavir because nevirapine substantially decreases atazanavir exposure and there is a potential risk for nevirapine-associated toxicity due to increased nevirapine exposures. Fosamprenavir ↓ Amprenavir ↑ Nevirapine Co-administration of nevirapine and fosamprenavir without ritonavir is not recommended.

Fosamprenavir/Ritonavir ↓ Amprenavir ↑ Nevirapine No dosing adjustments are required when nevirapine is co-administered with 700/100 mg of fosamprenavir/ritonavir twice daily. The combination of nevirapine administered with fosamprenavir/ritonavir once daily has not been studied. Indinavir ↓ Indinavir The appropriate doses of this combination of indinavir and nevirapine with respect to efficacy and safety have not been established. Lopinavir/Ritonavir ↓ Lopinavir Dosing in adult patients: A dose adjustment of lopinavir/ritonavir to 500/125 mg tablets twice daily or 533/133 mg (6.5 mL) oral solution twice daily is recommended when used in combination with nevirapine.

Neither lopinavir/ritonavir tablets nor oral solution should be administered once daily in combination with nevirapine. Dosing in pediatric patients: Please refer to the Kaletra ® prescribing information for dosing recommendations based on body surface area and body weight. Neither lopinavir/ritonavir tablets nor oral solution should be administered once daily in combination with nevirapine. Nelfinavir ↓ Nelfinavir M8 Metabolite ↓ Nelfinavir C min The appropriate doses of the combination of nevirapine and nelfinavir with respect to safety and efficacy have not been established.

Saquinavir/Ritonavir The interaction between nevirapine and saquinavir/ritonavir has not been evaluated The appropriate doses of the combination of nevirapine and saquinavir/ritonavir with respect to safety and efficacy have not been established. HIV Antiviral Agents: Non-Nucleoside Reverse Transcriptase Inhibitors (NNRTIs) Efavirenz ↓ Efavirenz The appropriate doses of these combinations with respect to safety and efficacy have not been established. Etravirine Rilpivirine Plasma concentrations may be altered. Nevirapine should not be co-administered with another NNRTI as this combination has not been shown to be beneficial.

Other Agents Analgesics: Methadone ↓ Methadone Methadone levels were decreased; increased dosages may be required to prevent symptoms of opiate withdrawal. Methadone-maintained patients beginning nevirapine therapy should be monitored for evidence of withdrawal and methadone dose should be adjusted accordingly. Antiarrhythmics: Amiodarone, disopyramide, lidocaine Plasma concentrations may be decreased. Appropriate doses for this combination have not been established. Antibiotics: Clarithromycin ↓ Clarithromycin ↑ 14-OH clarithromycin Clarithromycin exposure was significantly decreased by nevirapine; however, 14-OH metabolite concentrations were increased.

Because clarithromycin active metabolite has reduced activity against Mycobacterium avium-intracellulare complex , overall activity against this pathogen may be altered. Alternatives to clarithromycin, such as azithromycin, should be considered. Rifabutin ↑ Rifabutin Rifabutin and its metabolite concentrations were moderately increased. Due to high intersubject variability, however, some patients may experience large increases in rifabutin exposure and may be at higher risk for rifabutin toxicity. Therefore, caution should be used in concomitant administration.

Rifampin ↓ Nevirapine Nevirapine and rifampin should not be administered concomitantly because decreases in nevirapine plasma concentrations may reduce the efficacy of the drug. Physicians needing to treat patients co-infected with tuberculosis and using a nevirapine-containing regimen may use rifabutin instead. Anticonvulsants: Carbamazepine, clonazepam, ethosuximide Plasma concentrations of nevirapine and the anticonvulsant may be decreased. Use with caution and monitor virologic response and levels of anticonvulsants.

Antifungals: Fluconazole ↑ Nevirapine Because of the risk of increased exposure to nevirapine, caution should be used in concomitant administration, and patients should be monitored closely for nevirapine-associated adverse events. Ketoconazole ↓ Ketoconazole Nevirapine and ketoconazole should not be administered concomitantly because decreases in ketoconazole plasma concentrations may reduce the efficacy of the drug. Itraconazole ↓ Itraconazole Nevirapine and itraconazole should not be administered concomitantly due to potential decreases in itraconazole plasma concentrations that may reduce efficacy of the drug. Antithrombotics: Warfarin Plasma concentrations may be increased.

Potential effect on anticoagulation. Monitoring of anticoagulation levels is recommended. Calcium Channel blockers: Diltiazem, nifedipine, verapamil Plasma concentrations may be decreased. Appropriate doses for these combinations have not been established. Cancer Chemotherapy: Cyclophosphamide Plasma concentrations may be decreased. Appropriate doses for this combination have not been established. Ergot Alkaloids: Ergotamine Plasma concentrations may be decreased. Appropriate doses for this combination have not been established. Immunosuppressants: Cyclosporine, tacrolimus, sirolimus Plasma concentrations may be decreased. Appropriate doses for these combinations have not been established.

Motility Agents: Cisapride Plasma concentrations may be decreased. Appropriate doses for this combination have not been established. Opiate Agonists: Fentanyl Plasma concentrations may be decreased. Appropriate doses for this combination have not been established. Oral Contraceptives: Ethinyl estradiol and Norethindrone ↓ Ethinyl Estradiol ↓ Norethindrone Despite lower ethinyl estradiol and norethindrone exposures when co-administered with nevirapine, literature reports suggest that nevirapine has no effect on pregnancy rates among HIV-infected women on combined oral contraceptives.

When co-administered with nevirapine, no dose adjustment of ethinyl estradiol or norethindrone is needed when used in combination for contraception. When these oral contraceptives are used for hormonal regulation during nevirapine therapy, the therapeutic effect of the hormonal therapy should be monitored. Co-administration of nevirapine can alter the concentrations of other drugs and other drugs may alter the concentration of nevirapine. The potential for drug interactions must be considered prior to and during therapy. ( 5.4 , 7 , 12.3 ) Drug Interactions [see Drug Interactions (7) ] Nevirapine induces hepatic cytochrome P450 metabolic isoenzymes 3A and 2B6.

Co-administration of nevirapine and drugs primarily metabolized by CYP3A or CYP2B6 may result in decreased plasma concentrations of these drugs and attenuate their therapeutic effects. While primarily an inducer of cytochrome P450 3A and 2B6 enzymes, nevirapine may also…

8.1 Pregnancy Pregnancy Exposure Registry There is a pregnancy registry that monitors pregnancy outcomes in women exposed to nevirapine during pregnancy. Healthcare providers are encouraged to register patients by calling the Antiretroviral Pregnancy Registry (APR) at 1-800-258-4263. Risk Summary Available data from the APR show no difference in the risk of overall major birth defects for nevirapine compared with the background rate for major birth defects of 2.7% in the U.S. reference population of the Metropolitan Atlanta Congenital Defects Program (MACDP) [see Data ] . The rate of miscarriage is not reported in the APR.

The estimated background rate of miscarriage in clinically recognized pregnancies in the U.S. general population is 15-20%. The background risk of birth defects and miscarriage for the indicated population is unknown. Methodological limitations of the APR include the use of MACDP as the external comparator group. The MACDP population is not disease-specific, evaluates women and infants from a limited geographic area, and does not include outcomes for births that occurred at < 20 weeks gestation. In literature reports, immediate-release nevirapine exposure (C min ) can be up to 29% lower during pregnancy.

However, as this reduction was not found to be clinically meaningful, dose adjustment is not necessary [see Data ] . There is a risk for severe hepatic events in pregnant women exposed to nevirapine [see Clinical Considerations ]. In animal reproduction studies, no evidence of adverse developmental outcomes was observed following oral administration of nevirapine during organogenesis in the rat and rabbit, at systemic exposures (AUC) to nevirapine approximately equal (rats) and 50% higher (rabbits) than the exposure in humans at the recommended 400 mg daily dose [see Data ].

Clinical Considerations Maternal Adverse Reactions Severe hepatic events, including fatalities, have been reported in pregnant women receiving chronic nevirapine therapy as part of combination treatment of HIV-1 infection. Regardless of pregnancy status, women with CD4 + cell counts greater than 250 cells/mm 3 should not initiate nevirapine unless the benefit outweighs the risk. It is unclear if pregnancy augments the risk observed in non-pregnant women [see Warnings and Precautions (5.1) ] .

Data Human Data Based on prospective reports to the APR of exposures to nevirapine during pregnancy resulting in live births (including over 1100 exposed in the first trimester and over 1500 exposed in the second/third trimester), the prevalence of birth defects in live…