LC–MS/MS determination of etravirine in rat plasma and its application in pharmacokinetic studies

Etravirine is a non-nucleoside reverse transcriptase inhibitor (NNRTI) that is active against NNRT-resistant HIV-1. A simple, sensitive, and specific LC–MS/MS method was developed and validated for the analysis of etravirine in rat plasma using itraconazole as the internal standard. The analytes were extracted with ethyl acetate and chromatographed on a reverse-phase XTerra MS C18 column. Elution was achieved with a mobile phase gradient varying the proportion of a 2 mM ammonium acetate aqueous solution containing 0.1% formic acid (solvent A) and a 0.1% formic acid in methanol solution (solvent B) at a flow rate of 300 μL/min. The analytes were monitored by tandem-mass spectrometry with positive electrospray ionization. The precursor/product transitions (m/z) in the positive ion mode were 435.9 → 163.6 and 706.7 → 392.6 for etravirine and the internal standard, respectively. Calibration curves were linear over the etravirine rat plasma concentration range of 1–100 ng/mL. The inter- and intra-day accuracy and precision were within ±10%. The assay has been successfully used for pharmacokinetic evaluation of etravirine using the rat as an animal model.