Drug Interactions between atazanavir and efavirenz / lamivudine / tenofovir disoproxil

ADJUST DOSE: Coadministration with efavirenz may significantly decrease the plasma concentrations of atazanavir. Plasma concentrations of cobicistat, a pharmacokinetic enhancer given concomitantly with atazanavir, may also be reduced. Reduced atazanavir plasma levels may lead to diminished virologic response and possible resistance to atazanavir. The mechanism is efavirenz induction of CYP450 3A4, the isoenzyme responsible for the metabolic clearance of atazanavir and cobicistat. In 27 subjects, efavirenz (600 mg once a day for 14 days) decreased the mean steady-state peak plasma concentration (Cmax), systemic exposure (AUC), and trough plasma concentration (Cmin) of atazanavir (400 mg once a day) by 59%, 74%, and 93%, respectively, compared to administration of atazanavir alone. When ritonavir 100 mg was added to the regimen and given simultaneously with atazanavir 300 mg once a day in 13 study subjects, daily administration of efavirenz 600 mg two hours later resulted in atazanavir systemic exposure that was similar to that produced by 400 mg of atazanavir alone. Atazanavir boosted with cobicistat appears more sensitive to the effects of CYP450 3A4 induction by efavirenz than atazanavir boosted with ritonavir; however, pharmacokinetic data are not available.

MANAGEMENT: Concomitant use of efavirenz with unboosted atazanavir, atazanavir-ritonavir, or atazanavir-cobicistat is not generally recommended in either treatment-naive or treatment-experienced patients. Some authorities consider the administration of atazanavir-cobicistat with efavirenz to be contraindicated. However if considered necessary in treatment-naive patients, a prescription of atazanavir 400 mg-ritonavir 100 mg or atazanavir 400 mg-cobicistat 150 mg once daily with food, and efavirenz 600 mg administered once daily on an empty stomach at bedtime, may be considered. Other authorities have also recommended atazanavir 400 mg-ritonavir 200 mg and efavirenz 600 mg, all as a single daily dose with food and close clinical monitoring.

MONITOR: Coadministration of efavirenz with other agents known to induce hepatotoxicity may potentiate the risk of liver injury. Efavirenz has been associated with hepatotoxicity during postmarketing use. Among reported cases of hepatic failure, a few occurred in patients with no preexisting hepatic disease or other identifiable risk factors.

MANAGEMENT: The risk of hepatic injury should be considered when efavirenz is used in combination with other agents that are potentially hepatotoxic (e.g., acetaminophen; alcohol; androgens and anabolic steroids; antituberculous agents; azole antifungal agents; ACE inhibitors; cyclosporine (high dosages); disulfiram; endothelin receptor antagonists; interferons; ketolide and macrolide antibiotics; kinase inhibitors; minocycline; nonsteroidal anti-inflammatory agents; other HIV reverse transcriptase inhibitors; proteasome inhibitors; retinoids; sulfonamides; tamoxifen; thiazolidinediones; tolvaptan; vincristine; zileuton; anticonvulsants such as carbamazepine, hydantoins, felbamate, and valproic acid; lipid-lowering medications such as fenofibrate, lomitapide, mipomersen, niacin, and statins; herbals and nutritional supplements such as black cohosh, chaparral, comfrey, DHEA, kava, pennyroyal oil, and red yeast rice). Patients should be advised to seek medical attention if they experience potential signs and symptoms of hepatotoxicity such as fever, rash, itching, anorexia, nausea, vomiting, fatigue, malaise, right upper quadrant pain, dark urine, pale stools, and jaundice. Monitoring of liver function tests should occur before and during treatment, especially in patients with underlying hepatic disease (including hepatitis B or C coinfection) or marked transaminase elevations. The benefit of continued therapy with efavirenz should be considered against the unknown risks of significant liver toxicity in patients who develop persistent elevations of serum transaminases greater than five times the upper limit of normal.

MONITOR: Coadministration of efavirenz with other agents known to induce hepatotoxicity may potentiate the risk of liver injury. Efavirenz has been associated with hepatotoxicity during postmarketing use. Among reported cases of hepatic failure, a few occurred in patients with no preexisting hepatic disease or other identifiable risk factors.

MANAGEMENT: The risk of hepatic injury should be considered when efavirenz is used in combination with other agents that are potentially hepatotoxic (e.g., acetaminophen; alcohol; androgens and anabolic steroids; antituberculous agents; azole antifungal agents; ACE inhibitors; cyclosporine (high dosages); disulfiram; endothelin receptor antagonists; interferons; ketolide and macrolide antibiotics; kinase inhibitors; minocycline; nonsteroidal anti-inflammatory agents; other HIV reverse transcriptase inhibitors; proteasome inhibitors; retinoids; sulfonamides; tamoxifen; thiazolidinediones; tolvaptan; vincristine; zileuton; anticonvulsants such as carbamazepine, hydantoins, felbamate, and valproic acid; lipid-lowering medications such as fenofibrate, lomitapide, mipomersen, niacin, and statins; herbals and nutritional supplements such as black cohosh, chaparral, comfrey, DHEA, kava, pennyroyal oil, and red yeast rice). Patients should be advised to seek medical attention if they experience potential signs and symptoms of hepatotoxicity such as fever, rash, itching, anorexia, nausea, vomiting, fatigue, malaise, right upper quadrant pain, dark urine, pale stools, and jaundice. Monitoring of liver function tests should occur before and during treatment, especially in patients with underlying hepatic disease (including hepatitis B or C coinfection) or marked transaminase elevations. The benefit of continued therapy with efavirenz should be considered against the unknown risks of significant liver toxicity in patients who develop persistent elevations of serum transaminases greater than five times the upper limit of normal.

ADJUST DOSE: Coadministration with tenofovir may decrease the plasma concentrations of unboosted atazanavir. The mechanism of the interaction has not been described. Reduced atazanavir plasma levels may lead to diminished virologic response and possible resistance to atazanavir. In healthy subjects, tenofovir (300 mg once daily) decreased the systemic exposure (AUC) and trough plasma concentration (Cmin) of unboosted atazanavir (400 mg once daily) by 25% and 40%, respectively, compared to administration of atazanavir alone. When ritonavir was added as a booster and given simultaneously with atazanavir 300 mg once daily and tenofovir to HIV-infected subjects, the AUC and Cmin of atazanavir were approximately 2.3- and 4-fold higher, respectively, than the values observed for unboosted atazanavir in healthy subjects.

MONITOR: The use of atazanavir boosted with either cobicistat or ritonavir may increase tenofovir plasma concentrations. Increased tenofovir plasma concentrations may increase the risk for tenofovir-related renal adverse effects, including renal impairment, renal failure, elevated creatinine, and Fanconi syndrome. The mechanism of this interaction has not been described. Cobicistat may decrease estimated creatinine clearance via inhibition of tubular secretion of creatinine; however, renal glomerular function does not appear to be affected. When given concomitantly with atazanavir 300 mg and ritonavir 100 mg once daily, the AUC and Cmin of tenofovir increased by 37% and 29%, respectively. When given concomitantly with cobicistat, the AUC and Cmin of tenofovir was also increased by 23% and 55%, respectively. Data are lacking to determine whether concomitant use of tenofovir with cobicistat-containing regimens is associated with a greater risk of renal complications compared with regimens that do not include cobicistat.

MANAGEMENT: Administration of unboosted atazanavir with tenofovir is not recommended. In patients requiring combination therapy with atazanavir and tenofovir, it is recommended that tenofovir 300 mg be administered with either atazanavir 300 mg-ritonavir 100 mg or atazanavir 300 mg-cobicistat 150 mg, all as a single daily dose with food. Initiation of cobicistat or cobicistat-containing regimens is not recommended in patients with CrCl less than 70 mL/min if any coadministered medicine requires dose adjustment based on renal function (including tenofovir) or is nephrotoxic. If concomitant therapy is necessary, monitoring of renal function is recommended, particularly in patients with risk factors for renal impairment.