Rapid and Specific Liquid Chromatographic Tandem Mass Spectrometric Determination of Tenofovir in Human Plasma and its Fragmentation Study

A simple, specific, and high throughput liquid chromatography tandem mass spectrometry method is developed for the determination of tenofovir, a nucleotide reverse transcriptase inhibitor, in human plasma using adefovir as internal standard. Plasma samples are prepared by solid-phase extraction of the analyte and internal standard using Waters Oasis MCX cartridges (1 cc, 30 mg). The chromatographic separation is achieved on a reversed-phase Chromolith, C18 analytical column (100 mmx4.6 mm, 5 microm) under isocratic conditions. The mobile phase consists of 0.5% formic acid in water and acetonitrile (90:10, v/v) to give a run time of 1.8 min. The protonated precursor-->product ion transitions for tenofovir and IS are monitored on a triple quadrupole mass spectrometer, operating in the multiple reaction monitoring and positive ion mode. The fragmentation pathways for tenofovir are studied by varying the collision energy (5-55 V) using nitrogen as CAD gas. A linear dynamic range of 3.1-1002.0 ng/mL is established using 0.2 mL plasma sample. The method is fully validated for its sensitivity, selectivity, accuracy and precision, matrix effect, recovery, stability, and dilution integrity. It is applied to a bioequivalence study in 43 human subjects after oral administration of 300 mg tablet formulation under fasting conditions.