An LC–MS/MS method for the simultaneous determination of goserelin and testosterone in rat plasma for pharmacokinetic and pharmacodynamic studies

• The simultaneous determination of goserelin and testosterone in a single assay has been realized.
• The LLOQ for goserelin is 0.01 ng/mL, which is more sensitive than previously reported methods.
• The difference of the intrinsic polarities between the two compounds was overcome.
• The pharmacokinetic and pharmacodynamic datas were obtained from the same plasma sample.

A liquid chromatography–electrospray ionization tandem mass spectrometry (LC–ESI-MS/MS) method was developed, using testosterone-d3 as a surrogate analyte, for the simultaneous quantification of goserelin and testosterone in rat plasma. According to this method, the pharmacokinetic and pharmacodynamic data were obtained from a single plasma sample aliquot. The method involved the addition of alarelin as an internal standard (IS) for goserelin and testosterone-13C3 for testosterone or testosterone-d3. The conditions for the separation of these two compounds were achieved on a ZORBAX Eclipse Plus C18 column (Agilent, 2.1 × 50 mm, 1.8 μm, Stockport, UK) in a single chromatographic run at a flow rate of 400 μL/min. In order to minimize interferences of complex matrix, the extraction of plasma consisted of a protein precipitation step using methanol, followed by purification using an Oasis® HLB solid-phase extraction column. The method was validated in the concentration range of 0.01–30.0 ng/mL for goserelin and 0.05–30.0 ng/mL for testosterone-d3, respectively. The within- and between-run precisions were 1.7–9.2% and 2.1–6.9%, respectively. The within- and between-run accuracies were −1.8 to 5.3% and −4.9 to 4.0%, respectively. This accurate and highly specific assay provides a useful method to evaluate the pharmacokinetics and pharmacodynamics of goserelin in rats.