Performance analysis of a rapid HPLC determination with the solvent demixing extraction of HIV antiproteases and efavirenz in plasma.

A rapid and simple high-performance liquid chromatographic method without internal standardization is evaluated for the drug-level monitoring of most marketed antiproteases and efavirenz. Following plasma deproteinization with acetonitrile, the analytes are extracted into the solvent while it is demixed by the addition of a saturating amount of neutral salt. The organic supernatant is diluted by half with water up to the polarity of the mobile phase before being injected. The isocratic mobile phase is unbuffered water-acetonitrile (52:48), and the stationary phase is LiChrospher 100 RP-8 (5 microm). Analytes are eluted between 4 min (amprenavir and indinavir) and 20 min (nelfinavir). A spreadsheet program including analysis of variance (ANOVA) and regression is used for both the overall validation of milligrams-per-liter determinations and the performance evaluation of analytical steps from chromatographic raw data. Extraction shows acceptable 5% repeatability and nearly 100% recovery, although it is somewhat concentration-dependent. The calibration function is better fitted by bilogarithmic than arithmetical regression, and the ANOVA of raw data is found quite predictive of the quality of the final determinations.