Efavirenz

Absorption

Efavirenz, Emtricitabine and Tenofovir Disoproxil Fumarate
: One efavirenz, emtricitabine and tenofovir disoproxil fumarate tablet is bioequivalent to one Sustiva tablet (600 mg) plus one EMTRIVA® capsule (200 mg) plus one VIREAD® tablet (300 mg) following single-dose administration to fasting healthy subjects (N=45).
Efavirenz: In HIV-1 infected subjects time-to-peak plasma concentrations were approximately 3 to 5 hours and steady-state plasma concentrations were reached in 6 to 10 days. In 35 HIV-1 infected subjects receiving EFV 600 mg once daily, steady-state Cmax was 12.9 ± 3.7 µM (mean ± SD), Cmin was 5.6 ± 3.2 µM, and AUC was 184 ± 73 µM•hr. EFV is highly bound (approximately 99.5 to 99.75%) to human plasma proteins, predominantly albumin. Following administration of 14C-labeled EFV, 14 to 34% of the dose was recovered in the urine (mostly as metabolites) and 16 to 61% was recovered in feces (mostly as parent drug). In vitro studies suggest CYP3A and CYP2B6 are the major isozymes responsible for EFV metabolism. EFV has been shown to induce CYP enzymes, resulting in induction of its own metabolism. EFV has a terminal half-life of 52 to 76 hours after single doses and 40 to 55 hours after multiple doses.
Emtricitabine: Following oral administration, FTC is rapidly absorbed, with peak plasma concentrations occurring at 1 to 2 hours postdose. Following multiple dose oral administration of FTC to 20 HIV-1 infected subjects, the steady-state plasma FTC Cmax was 1.8 ± 0.7 mcg/mL (mean ± SD) and the AUC over a 24-hour dosing interval was 10.0 ± 3.1 mcg•hr/mL. The mean steady-state plasma trough concentration at 24 hours postdose was 0.09 mcg/mL. The mean absolute bioavailability of FTC was 93%. Less than 4% of FTC binds to human plasma proteins in vitro, and the binding is independent of concentration over the range of 0.02 to 200 mcg/mL. Following administration of radiolabelled FTC, approximately 86% is recovered in the urine and 13% is recovered as metabolites. The metabolites of FTC include 3′-sulfoxide diastereomers and their glucuronic acid conjugate. FTC is eliminated by a combination of glomerular filtration and active tubular secretion with a renal clearance in adults with normal renal function of 213 ± 89 mL/min (mean ± SD). Following a single oral dose, the plasma FTC half-life is approximately 10 hours.
Tenofovir DF: Following oral administration of a single 300 mg dose of TDF to HIV-1 infected subjects in the fasted state, maximum serum concentrations (Cmax) were achieved in 1.0 ± 0.4 hrs (mean ± SD) and Cmax and AUC values were 296 ± 90 ng/mL and 2287 ± 685 ng•hr/mL, respectively. The oral bioavailability of tenofovir from TDF in fasted subjects is approximately 25%. Less than 0.7% of tenofovir binds to human plasma proteins in vitro, and the binding is independent of concentration over the range of 0.01 to 25 mcg/mL. Approximately 70 to 80% of the intravenous dose of tenofovir is recovered as unchanged drug in the urine. Tenofovir is eliminated by a combination of glomerular filtration and active tubular secretion, with a renal clearance in adults with normal renal function of 243 ± 33 mL/min (mean ± SD). Following a single oral dose, the terminal elimination half-life of tenofovir is approximately 17 hours.
Effects of Food on Oral Absorption
Efavirenz, emtricitabine and tenofovir disoproxil fumarate has not been evaluated in the presence of food. Administration of EFV tablets with a high-fat meal increased the mean AUC and Cmaxof EFV by 28% and 79%, respectively, compared to administration in the fasted state. Compared to fasted administration, dosing of TDF and FTC in combination with either a high-fat meal or a light meal increased the mean AUC and Cmax of tenofovir by 35% and 15%, respectively, without affecting FTC exposures [see Dosage and Administration (2.2) and Patient Counseling Information (17)].
Specific Populations
Race
Efavirenz: The pharmacokinetics of EFV in HIV-1 infe …