Factors associated with variability in rifampin plasma pharmacokinetics and the relationship between rifampin concentrations and induction of efavirenz clearance.

Study Objectives: To identify factors associated with variability in rifampin plasma pharmacokinetics and explore the relationship between rifampin pharmacokinetics and change in efavirenz plasma pharmacokinetics with rifampin coadministration.

Methods: In this randomized, cross-over study, 12 healthy volunteers received either efavirenz 600 mg/day or efavirenz 600 mg with rifampin 600 mg/day for 8 days. After a washout period of at least 2 weeks, subjects crossed over to the alternate 8-day regimen.