Determination of underivatised efaroxan and idazoxan in blood plasma by capillary gas chromatography with mass-selective detection

Validated method for the determination of idazoxan in human plasma by liquid chromatography with tandem mass spectrometric detection

A liquid chromatography-tandem mass spectrometry method for the determination of idazoxan in human (heparin) plasma is presented, which was developed and validated using 500 microl of sample. Sample preparation consisted of the addition of fluoroidazoxan as the internal standard, extraction at alkaline conditions into tert.-butyl methyl ether, followed by centrifugation, evaporation of the solvent and reconstitution in methanol. After a short chromatographic run, detection took place by ionspray tandem mass spectrometry in positive ion mode. Validation results on linearity, specificity, accuracy, precision and stability, as well as application of the method to samples from a clinical trial, are shown. The validated calibration range is from 0.300 to 100 ng/ml, with accuracy (bias) and precision (coefficient of variation) being below 15% at all levels. A sample throughput of, typically, 150 per day can be achieved.

Development of a radioimmunoassay for idazoxan hydrochloride

To facilitate the measurement of idazoxan in clinical trials an immunoassay capable of detecting low ng ml-1 concentrations was required. A stable derivative was prepared which, after linking to keyhole limpet hemocyanin (KLH), was subsequently immunized into sheep. Early assay development was carried out with both fluorescent (1-FITC) and iodinated (I-125) labels. The assay methodology was the same in both cases, using magnetizable solid-phase particles to which the antibody was linked. The sensitivity of the assay was such that a large sample volume was required, which in turn, led to problems of increased protein interference. The use of pepsin to digest the protein was used effectively after several blocking agents were unsuccessfully used. The limit of detection was in the region of 3 ng ml-1. Cross-reactivity studies showed that the antibody was specific for idazoxan. Intra- and inter-assay precision was 7 and 12%, respectively. Correlation with the analytical GC-MSD method was in the order of 0.90.