Quantification of the antipsychotics flupentixol and haloperidol in human serum by high-performance liquid chromatography with ultraviolet detection.

A high-performance liquid chromatography (HPLC) method was developed for quantification of both isomers of the thioxanthene neuroleptic flupentixol and of the butyrophenone derivative haloperidol in human serum. After extraction with diethyl ether-n-heptane (50:50, v/v), an isocratic normal-phase HPLC system with a Hypersil cyanopropyl silica column (250x4.6 mm, 5 microm particle size) was used with ultraviolet detection at 254 nm and elution with a mixture of 920 ml acetonitrile, 110 ml methanol, 30 ml 0.1 M ammonium acetate, and 50 microl triethylamine. The limit of quantitation of 0.5 ng/ml and 0.3 ng/ml for flupentixol and haloperidol, respectively, was sufficient to quantify both compounds in serum after administration of clinically adjusted doses. The suitability of the described method for therapeutic drug monitoring and clinical pharmacokinetic studies was assessed by analysis of more than 100 trough level serum samples.