The steady-state pharmacokinetics of efavirenz and nevirapine when used in combination in human immunodeficiency virus type 1-infected persons

The steady-state pharmacokinetics of efavirenz and nevirapine, when used in combination to treat human immunodeficiency virus type 1 (HIV-1)-infected subjects, were investigated. HIV-1-infected persons who had used efavirenz (600 mg once daily) for >/=2 weeks were eligible for study inclusion.

The plasma pharmacokinetics of efavirenz were determined over 24 h. Subsequently, nevirapine (400 mg once daily) was added to the regimen. After 4 weeks, the pharmacokinetics of efavirenz and nevirapine were assessed over 24 h. The differences between the pharmacokinetic parameters of efavirenz with and without nevirapine were analysed, and the pharmacokinetics of nevirapine were compared with those in historical control patients. The exposure to efavirenz when combined with nevirapine was significantly decreased by 22% (area under the plasma concentration vs. time curve), 36% (minimum plasma concentration), and 17% (maximum plasma concentration). Nevirapine pharmacokinetics appear to be unaffected by coadministration of efavirenz, compared with data from historical control patients.