Renal Impairment: The pharmacokinetics of efavirenz have not been studied in patients with renal insufficiency; however, less than 1% of efavirenz is excreted unchanged in the urine, so the impact of renal impairment on efavirenz elimination should be minimal.

Gender and Race: The pharmacokinetics of efavirenz in patients appear to be similar between men and women and among the racial groups studied.

Geriatric: (See PRECAUTIONS: Geriatric Use

Pediatrics: (See PRECAUTIONS: Pediatric Use)

Efavirenz has been shown in vivo to cause hepatic enzyme induction, thus increasing the biotransformation of some drugs metabolized by CYP3A4. In vitro studies have shown that efavirenz inhibited P450 isozymes 2C9, 2C19, and 3A4 with Ki values (8.5-17 µM) in the range of observed efavirenz plasma concentrations. In in vitro studies, efavirenz did not inhibit CYP2E1 and inhibited CYP2D6 and CYP1A2 (Ki values 82-160 µM) only at concentrations well above those achieved clinically. The effects on CYP3A4 activity are expected to be similar between 200-mg, 400-mg, and 600-mg doses of efavirenz. Coadministration of efavirenz with drugs primarily metabolized by 2C9, 2C19, and 3A4 isozymes may result in altered plasma concentrations of the coadministered drug. Drugs which induce CYP3A4 activity would be expected to increase the clearance of efavirenz resulting in lowered plasma concentrations.

Drug interaction studies were performed with efavirenz and other drugs likely to be coadministered or drugs commonly used as probes for pharmacokinetic interaction. The effects of coadministration of efavirenz on the AUC and C_max are summarized in Table 1 (effect of efavirenz on other drugs) and Table 2 (effect of other drugs on efavirenz). For information regarding clinical recommendations see PRECAUTIONS: Drug Interactions.

↑Indicates increase ↓Indicates decrease « Indicates no change
^aCompared with atazanavir 400 mg qd alone.
^bComparator dose of indinavir was 800 mg q8h x 10 days. Mean decreases in the C_min of indinavir ranged from 39 to 57%.
^cParallel-group design; n for efavirenz + lopinavir/ritonavir, n for lopinavir/ritonavir alone.
^dC_min of lopinavir was significantly decreased by 39%. The pharmacokinetics of ritonavir 100 mg q12h are unaffected by concurrent efavirenz.
^eSoft Gelatin Capsule.
^f90% CI not available.

Brand Name: Sustiva
Generic Name: Efavirenz

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