Determination of ospemifene in human plasma by LC-MS/MS and its application to a human pharmacokinetic study

A highly sensitive, specific and rapid liquid chromatography-tandem mass spectrometry (LC-MS/MS) analytical method has been developed and validated for the determination of ospemifene in human plasma using ospemifene-d₄ as an internal standard. Solid-phase extraction technique with Phenomenex Strata X-33 μm polymeric sorbent cartridges (30 mg/1 mL) was used to extract the analytes from the plasma. The chromatographic separation was achieved on Agilent Eclipse XDB-Phenyl, 4.6 × 75 mm, 3.5 μm column using the mobile phase composition of methanol and 20 mm ammonium formate buffer (90:10, v/v) at a flow rate of 0.9 mL/min. A detailed method validation was performed as per the US Food and Drug Administration guidelines and the calibration curve obtained was linear (r²  = 99) over the concentration range 5.02-3025 ng/mL. The API-4500 MS/MS was operated under multiple reaction monitoring mode during the analysis. The proposed method was successfully applied to a pharmacokinetic study in healthy human volunteers after oral administration of an ospemifene 60 mg tablet under fed conditions.