Drug Interactions between darunavir and Symfi Lo

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.

MONITOR: Coadministration with efavirenz may decrease the plasma concentrations of darunavir, even in the presence of cobicistat or low-dose ritonavir as a pharmacokinetic booster. Additionally, the plasma concentration of cobicistat may be reduced. Reduced darunavir plasma levels may lead to diminished virologic response and possible resistance to darunavir. The mechanism is efavirenz induction of CYP450 3A4, the isoenzyme responsible for the metabolic clearance of darunavir and cobicistat. In 12 study subjects, administration of darunavir/ritonavir (300 mg/100 mg twice a day) with efavirenz (600 mg once a day) decreased the peak plasma concentration (Cmax), area under the concentration-time curve (AUC) and trough plasma concentration (Cmin) of darunavir by 15%, 13% and 31%, respectively, compared to administration without efavirenz. In contrast, efavirenz Cmax, AUC, and Cmin increased by 15%, 21%, and 17%, respectively, in the presence of darunavir/ritonavir. The clinical significance of these changes are unknown. Data are not available for darunavir-cobicistat.

MANAGEMENT: Caution is advised if darunavir-ritonavir is coadministered with efavirenz. Antiretroviral response should be monitored closely and darunavir-ritonavir dose adjusted if necessary. Some authorities recommend a dose adjustment of darunavir 600 mg-ritonavir 100 mg twice daily. Concomitant use of darunavir-cobicistat with efavirenz is not recommended.

MONITOR: Coadministration of tenofovir and darunavir-ritonavir or darunavir-cobicistat may result in increased plasma concentrations of tenofovir and darunavir. Increased tenofovir plasma concentration 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 is unknown; however, increased tenofovir concentrations may be related to inhibition of P-glycoprotein by darunavir, cobicistat, or ritonavir in the renal tubules. Cobicistat may decrease estimated creatinine clearance via inhibition of tubular secretion of creatinine; however, renal glomerular function does not appear to be affected. In 12 study subjects, administration of darunavir-ritonavir (300 mg-100 mg twice daily) with tenofovir (300 mg once daily) increased the systemic exposure (AUC) and trough plasma concentration (Cmin) of darunavir by 21% and 24%, respectively, compared to administration without tenofovir. Tenofovir AUC and Cmin also increased by 22% and 37%, respectively, in the presence of darunavir-ritonavir. 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: Caution and close monitoring of renal function is recommended if darunavir-ritonavir or darunavir-cobicistat is to be used in combination with tenofovir, particularly in patients with risk factors for renal impairment. No dose adjustments appear necessary during coadministration of darunavir-ritonavir with tenofovir. However, 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.