An Open-label, Drug Interaction Study to Investigate the Effects of Steady-State Fenofibric Acid on the Single-Dose Pharmacokinetics of Efavirenz in Healthy Subjects

Efavirenz is predominantly metabolized by cytochrome P450 (CYP) 2B6. Fenofibric Acid is an inhibitor of CYP2B6. This study will evaluate the effect of multiple doses of fenofibric acid at steady-state on the pharmacokinetics of single-dose efavirenz in healthy adult subjects. This study will not evaluate the the effects of efavirenz on fenofibric acid pharmacokinetics. On study Day 1 after a fast of at least 10 hours, thirty healthy, non-smoking, non-obese, non-pregnant adult volunteers between the ages of 18 and 45 will be given one oral dose of efavirenz (1 x 600 mg tablet). Fasting will continue for 4 hours after the dose. Blood samples will be drawn from all participants before dosing and for 24 hours post-dose on a confined basis at times sufficient to adequately define the pharmacokinetics of efavirenz. Blood sampling will then continue on a non-confined basis at 48, 72, 96 and 120 hours post-dose. A 21 day washout period will be completed after the first dose of efavirenz on Day 1. On Days 22 through 30, all subjects will receive a single oral dose of fenofibric acid (1 x 105 mg tablet) in the morning without regard to meals. On the morning of Day 31 after a fast of at least 10 hours, all study participants will receive co-administered single oral doses of efavirenz (1 x 600 mg tablet) and fenofibric acid (1 x 105 mg tablet). Fasting will continue for 4 hours after the dose. Blood samples will be drawn from all participants before dosing and for 24 hours post-dose on a confined basis at times sufficient to adequately determine the pharmacokinetics of efavirenz. Blood sampling will then continue on a non-confined basis at 48, 72, 96 and 120 hours post-dose. A further goal of this study is to evaluate the safety and tolerability of this regimen in healthy volunteers. Subjects will be monitored throughout participation in the study for adverse reactions to the study drug and/or procedures. Vital signs (seated blood pressure and pulse) will be measured prior to dosing and at approximately 1, 2, 3 and 5 hours post-dose on Days 1, 22 and 31 to coincide with peak plasma concentrations of both efavirenz and fenofibric acid. Blood pressure and pulse will also be obtained at 24 hours post-dose on Days 2 and 32 prior to discharge from the clinical study unit. All adverse events whether elicited by query, spontaneously reported, or observed by clinic staff will be evaluated by the Investigator and reported in the subject's case report form.