Fluorimetric determination of some thioxanthene derivatives in dosage forms and biological fluids.

A simple and highly sensitive method is proposed for the fluorimetric determination of four thioxanthene derivatives, namely: chlorprothixene, clopenthixol, flupentixol and thiothixene, in dosage forms and biological fluids. The method involves the use of nitrous acid as an oxidant to produce the corresponding fluorescent thioxanthenone sulphoxides. The experimental parameters were carefully studied and incorporated into the procedures. The results obtained compare favourably with those obtained by the official methods. The concentration-fluorescence plots were rectilinear over the range of 0.04-0.4 microg/ml for thiothixene, and 0.02-0.25 microg/ml for the other compounds, with minimum detectability (S/N = 2) of 2 ng/ml for all the studied compounds except thiothixene which was 4 ng/ml. The proposed method was applied to the determination of the studied compounds in dosage forms. The results obtained were in good agreement with those obtained adopting the USP XIII method. The proposed method was further applied to the determination of flupentixol in spiked human urine and plasma, the percentage recoveries were 94.39 +/- 1.81 and 96.46 +/- 0.28, respectively. A proposal of the reaction pathway was presented.

Determination of 3-(5-tetrazolyl) thioxanthone 10,10-dioxide in human plasma, urine and faeces.

A gas chromatographic method is described for assay of 3-(5-tetrazolyl) thioxanthone 10,10-dioxide (BW 59C) in human plasma, urine and faeces. After extraction into 1,2-dichloroethane from alkaline medium the compound is converted to the heptafluorobutyrate derivative which is injected into a gas chromatograph and measured using a 63Ni electron capture detector. The assay produces a linear calibration curve over the range 0-30 mug/ml when the internal standard method is used. Reproducibility is good and sensitivity down to 1 ng injected on column is possible. The method has been used to investigate the pharmacokinetic properties of BW 59C in man and has been semi-automated by the use of an autosampler and dedicated computer.