Simultaneous quantification of emtricitabine and tenofovir in human plasma using high-performance liquid chromatography after solid phase extraction

An accurate, sensitive and simple reverse-phase (RP) high-performance liquid chromatography (HPLC) assay for the simultaneous quantitative determination of emtricitabine and tenofovir in human blood plasma is described. Using 200 μL of plasma and BOND ELUT-C18 Varian columns, the solid phase extraction (SPE) method results in a clean baseline and high extraction efficiencies (100% for emtricitabine and 98.6% for tenofovir). An Atlantis™ dC-18 analytical column is used along with an 18 min linear gradient elution of phosphate buffer (pH 5.7) and methanol to provide sharp peaks for emtricitabine at 280 nm, tenofovir at 259 nm, and the internal standard 2′,3′didoxyuridine (DDU) at 262 nm. The method was validated over the range of 10-10,000 ng/mL for both analytes, and is accurate (average accuracies of three different concentrations ranged from 98 to 105% for emtricitabine and 97 to 103% for tenofovir) and precise (within- and between-day precision ranged from 1.7 to 3.7% and 3.7 to 5.2%, respectively). This method is suitable for use in clinical pharmacokinetic studies and is nimble enough for therapeutic drug monitoring.