Clomiphene citrate is first line therapy of female infertility but is also frequently abused by athletes. Human biotransformation of clomiphene results in numerous phase 1 and phase 2 metabolites. The involvement of the polymorphic cytochrome P450 2D6 leads to a high inter-individual variability. To comprehensively investigate clomiphene metabolism in vivo we established a highly sensitive and specific UPLC-MS/MS method for the stereoselective quantification of clomiphene and its phase 1 and phase 2 metabolites in plasma and urine. Reference compounds and stable isotope labelled internal standards were synthesized in-house. High-throughput sample preparation was done by protein precipitation. Analytes were separated by UPLC on a C18 column (1.8 μm, 2.1 * 100 mm) using a gradient of 0.1% formic acid in acetonitrile in 0.1% aqueous formic acid and detected by positive ESI-MS/MS in MRM mode. The lower limit of quantification was below 1 nM for all analytes. The method was validated according to recent guidelines. However, due to absorption effects during sampling the quantification of metabolites in urine was limited to phase 2 metabolites. The method was successfully applied to determine the pharmacokinetic of (E)- and (Z)-clomiphene and 14 metabolites following a single dose of 100 mg clomiphene citrate in 3 healthy subjects and proofed to be an essential tool to comprehensively investigate the human biotransformation of clomiphene.
Keywords: Clomiphene; Glucuronide; Metabolite; Plasma; Sulfate; Urine.
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