Midazolam: radioimmunoassay for pharmacokinetic studies in man

A specific radioimmunoassay (RIA) for the determination of the new short-acting water soluble imidazo-1,4-benzodiazepine, midazolam, directly in plasma has been developed. Employing 3H-midazolam as the radioligand and a rabbit antiserum to a diazo conjugate of 5'-aminomidazolam and albumin, the method has a limit of sensitivity of 2 ng/ml of midazolam using a 20 microliters sample of plasma. The intra- and inter-assay coefficients of variation ranged from 4 to 7% and 13 to 15%, respectively. The specificity of the RIA was established by demonstrating good agreement with both EC-GC and GC-MS procedures in the analysis of multiple clinical plasma samples. The utility of the RIA for the pharmacokinetic evaluation of midazolam is illustrated with plasma concentration profiles of the drug obtained in subjects who had received midazolam intravenously, intramuscularly and orally.