LC-APCI-MS-MS Analysis of Zidovudine in Human Plasma, and Application to a Bioequivalence Study

The objective of this work was to establish a sensitive, simple, accurate, and reliable LC-APCI-MS-MS method for analysis of zidovudine in human plasma. Plasma samples were processed by protein precipitation with perchloric acid solution. Separation on a 250 mm × 4.6 mm, 5 μm particle, C₁₈ column was achieved by use of methanol-water 65:35 (v/v) containing 0.2% formic acid as mobile phase. Mass spectrometric quantification was performed in positive-ion multiple reaction monitoring (MRM) mode, by monitoring the m/z transitions 268.1 → 127.0 for zidovudine and m/z 248.1 → 121.0 for tinidazole (internal standard). The calibration plot was linear in the concentration range 1.638-6250 μg L⁻¹, and the lower limit of quantification (LLOQ) was 1.638 μg L⁻¹. Intra-day and inter-day precision (as RSD) for zidovudine at four quality-control levels was less than 15%, and accuracy was between 95.1 and 114.2%. The method enables simple, sensitive, and accurate analysis of zidovudine in human plasma, and was successfully used in a bioequivalence study of 48 healthy Chinese volunteers.