Quantitative determination of zidovudine diaryl phosphate triester pro-drugs in rat plasma by high-performance liquid chromatography–electrospray ionization tandem mass spectrometry

A rapid, simple, and sensitive high-performance liquid chromatography/electrospray ionization tandem mass spectrometry (HPLC/ESI–MS/MS) method was developed and validated for quantitative analysis of 3′-azido-3′-deoxythymidine (zidovudine, AZT) diaryl phosphate triester pro-drugs, in rat plasma using 2′,3′-dideoxy-2′3′-didehydrothymidine (d4T) as internal standard (IS). The analytes were extracted from rat plasma with methanol after protein precipitation. The compounds were separated by HPLC with gradient elution (on a Shim-pack VP-ODS C₁₈ analytical column using a mobile phase of methanol/10 mM ammonium acetate). All the analytes were detected in positive ion mode using multiple reaction monitoring (MRM). The method was validated and the specificity, linearity, lower limit of quantitation (LLOQ), precision, accuracy, recoveries and stability were determined. LLOQs were 10 ng mL⁻¹ for M1, M2, M3, M4, and M5, respectively. Correlation coefficient (r) values for the linear range of 10–10,000 ng mL⁻¹ were greater than 0.999 for all the analytes. The intra-day and inter-day precision and accuracy were higher than 7.13%. The relative and absolute recovery was above 72% and no matrix effects were observed for all the analytes. This validated method provides a modern, rapid, and robust procedure for the pharmacokinetic studies of the pro-drugs after intravenous administration to rats. Some important results of AZT diaryl phosphate triester pro-drugs concerning chemical effect on pharmacokinetic performance are also studied.