Determination of Dothiepin in Human Plasma by LC-ESI-MS and its Application to Bioequivalence Studies

An LC-MS method for the determination of dothiepin in human plasma was developed and validated. Sample preparation involved extraction with n-hexane: 2-propanol (95: 5). Separation was on an Ultimate XB C18 column (2.1 x 150 mm, 5 mu m). A single-quadrupole mass spectrometer with an electrospray interface was operated in the selected-ion monitoring mode to detect the [M+H](+) ions at m/z 296 for dothiepin and at m/z 278 for the internal standard (amitriptylene). The method demonstrated good linearity from 0.78 ng mL(-1) (the LOQ) to 100 ng mL(-1). The mean extraction recovery was 82.4% for dothiepin and and 84.2% for the internal standard. The intra-day and inter-day precision ranged from 8.5 to 11.4% and 9.7 to 12.1% (RSD), respectively. The method was successfully applied to bio-equivalence studies of dothiepin hydrochloride tablets to obtain the pharmacokinetic parameters.