Determination of amisulpride, a new benzamide derivative, in human plasma and urine by liquid-liquid extraction or solid-phase extraction in combination with high-performance liquid chromatography and fluorescence detection. application to pharmacokinetics.

Amisulpride (SOLIAN) belongs to the benzamide series and shows antischizophrenic and antidepressant (anti-dysthymic) properties in man. Two methods suitable for pharmacokinetic investigations are proposed for the determination of amisulpride in human plasma. For the liquid-liquid extraction (LLE) based method, the plasma, added with the internal standard (an amisulpride analogue) is alkalinised with NaOH and extracted with a diethyl ether-chloroform mixture. The organic phase is removed, evaporated to dryness and redissolved in an acidic phosphate-acetonitrile mixture that, after a back-washing step with n-hexane, is injected onto the HPLC column (C18 BDS type) connected with a fluorimetric detector. The second method is based on an automatic solid-phase extraction (SPE) performed on an ASPEC device. The plasma sample, diluted with a pH 9 borate buffer, is loaded onto a disposable SPE C18 100-mg column. The analytes of interest (amisulpride and internal standard), after two washing steps with different solvents, are recovered in pure methanol; after evaporation to dryness, the residue is dissolved in an acidic phosphate buffer and injected onto the chromatographic apparatus already described. The limit of quantitation (LOQ) is 0.5 ng ml-1 for both methods; a linear correlation between concentrations and detector response has been demonstrated in the range 0.5-640 ng ml-1 for LLE, which is the most used method; for SPE methods, less used, linearity has been assessed in the plasma range of 0.5-160 ng ml-1.