Determination of efavirenz in human plasma by high-performance liquid chromatography with ultraviolet detection

Efavirenz is a non-nucleoside reverse transcriptase inhibitor for the treatment of the HIV infection. A simple, high-performance liquid chromatographic method has been developed and validated for the quantitative determination of efavirenz in human plasma. The method involved solid-phase extraction of the drug and the internal standard (L-737,354) from 300 μl of human plasma. The analysis was via UV detection at 250 nm using a reversed-phase C₈ analytical column and a isocratic mobile phase consisting of phosphate buffer (pH 5.75)–acetonitrile that resolved the drug and internal standard from endogenous matrix components and potential coadministered drugs. Within- and between-day precisions were less than 8.6% for all quality control samples. The lower limit of quantification was 0.1 μg/ml. Recovery of efavirenz from human plasma was greater than 83%. This validated assay is being used in pharmacokinetic studies with efavirenz.