Determination of nevirapine and efavirenz in plasma using GC/MS in selected ion monitoring mode.

An accurate, selective, and sensitive method for the determination of the nonnucleoside reverse transcriptase inhibitors (NNRTIs) nevirapine (nvp) and efavirenz (efv) in human plasma using gas chromatography-mass spectroscopy in selected ion monitoring mode (GC/MS-SIM) was developed. Solid-phase extraction (SPE) gave extraction yields near 100% for both nvp and efv, and calibration curves were linear over the therapeutic concentration ranges. Variation of intraday and interday precision was below 5%. Intraday and interday inaccuracies varied between 0.6% and 10.4%. The lower limits of detection using a 200-microL plasma sample were 27 ng/mL for nvp and 26 ng/mL for efv, and the lower limits of quantification were 54 ng/mL and 72 ng/mL, respectively. The method was applied to the determination of nvp and efv in plasma specimens of 73 patients in HIV stage III or IV and on antiretroviral treatment in Kigali, Rwanda.