Determination of turosteride, a new inhibitor of 5α-reductase, in human plasma by high-performance liquid chromatography with ultraviolet detection

A sensitive and specific HPLC method for the determination of turosteride in human plasma was developed and validated. Turosteride was extracted from plasma with diethyl ether. Further purifications of the fraction extracted were performed sequentially by solid-phase extraction using a CN cartridge and by liquid—liquid partition between n-hexane and acetonitrile. Finally the acetonitrile solution containing the test compound was evaporated to dryness and the residue dissolved in the mobile phase, then injected onto the HPLC system. The chromatographic separation was performed isocratically by a reversed-phase column filled with ODS using a water—acetonitrile—methanol mixture. The eluate was monitored at 210 nm. No peak interfering with that of turosteride was observed when blank human plasma was assayed. Linearity was obtained in the turosteride concentration range of 5–1000 ng/ml plasma. Six calibration curves in plasma prepared and run on six different days showed correlation coefficients higher than 0.99 and good reproducibility of the slope (C.V.=4.3%). The intra-day precision, evaluated at three concentrations (in the low, mid and high range of the standard curve) and expressed as C.V., ranged from 0.81 to 13.25%. The inter-day precision evaluated at the same concentrations was better than 10.7%. The inter-day accuracy evaluated in the same samples and expressed as the ratio of found/added amount of turosteride ranged from 97.66 to 98.38%. The limit of quantitation was 5 ng/ml plasma. The HPLC method described was successfully employed for the determination of turosteride in plasma samples obtained during a phase I clinical trial with the test compound.