An LC–ESI–MS–MS Method for Quantification of Tenofovir Octadecyloxyethyl Ester in Rat Plasma and Its Application to a Pharmacokinetic Study

Abstract

Tenofovir octadecyloxyethyl ester (TOE) is a novel ester prodrug of tenofovir. It is currently developed as a promising antiviral preclinical candidate. A simple and sensitive liquid chromatography–tandem mass spectrometry (LC–MS–MS) method has been developed and validated to quantify TOE in rat plasma. The method involves a simple extraction of TOE and loratadine (internal standard) from rat plasma after protein precipitation. Chromatographic separation was performed on a C₁₈ column by isocratic elution with acetonitrile and 5 mM ammonium acetate containing 0.03% ammonium hydroxide (70:30, v/v), at a flow rate of 0.3 mL min⁻¹. MS detection was performed on an API 3000 triple quadrupole mass spectrometer operating in ESI positive ionization mode. Ions monitored in the multiple selected reaction monitoring mode were m/z 584→270 for TOE and m/z 383→337 for loratadine, respectively. A linear calibration curve was established over the concentration range from 12.5 to 2,500 ng mL⁻¹ (r ² = 0.9961) with the lower quantitative limit of 12.5 ng mL⁻¹. The inter- and intra-day RSD were all <9.61%, while the accuracy (RE) was within the range from −8.40 to 4.20%. This novel method has been successfully applied to a pharmacokinetic study to obtain the oral concentration–time profile of TOE in rats.