A rapid and validated HPLC method to quantify racecadotril metabolite, thiorphan, in human plasma using solid-phase extraction.

A HPLC method with UV detection was developed and validated for the determination of thiorphan in human plasma. Nevirapine was used as the internal standard. Separation was performed by a Waters sunfire C18 reversed-phase column maintained at 35 degrees C. The mobile phase was a mixture of 0.05 M phosphate buffer with the pH adjusted to 2.6 and acetonitrile (74:26, v/v) at a flow rate of 1.0 mL/min. The UV detector was set at 210 nm. An original pre-treatment of plasma samples was developed, based on solid-phase extraction (SPE) with solid-phase extraction cartridges (Oasis HLB 3 mL, 60 mg). The extraction recovery for plasma samples of thiorphan at 0.1, 0.4 and 2.0 microg/mL was 93.5%, 98.2% and 97.8%, respectively. The calibration curve was linear with the correlation coefficient (r) above 0.9998. Linearity was verified over the range of 0.05-4 microg/mL thiorphan in plasma. The limit of quantification (LOQ) is 0.05 microg/mL. The mean accuracy was 92.7-99.6%. The coefficient of variation (precision) in the within- and between-batch was 2.2-8.4% and 4.1-8.1%, respectively. This method is simple, economical and specific, and has been used successfully in a pharmacokinetic study of thiorphan.