Assay of midazolam and brotizolam in plasma by a gas chromatographic and a radioreceptor technique.

A gas chromatographic method (GLC) using a capillary column, electron capture (EC) detection and a solid injection system for the determination of midazolam and brotizolam in plasma is described. Furthermore, the application of a radioreceptor technique (RRA), using a dry and stable benzodiazepine receptor preparation and 3H-flunitrazepam as a labelled ligand for the assay of both drugs is presented. A comparison was made between the RRA and the GLC method. For the gas chromatographic method, linear calibration graphs (r greater than 0.995) was obtained in the range of 0.1 -0.5 ng of brotizalam, and 1.0-5.0 ng of midazolam. Differences between duplicates were less than 8%. The relative affinity of the 1-hydroxymethyl and 4-hydroxy metabolites of brotizolam and midazolam were 0.33 and 0.14 respectively for brotizolam and 0.64 and 0.23 for midazolam. Extraction yields of parents drugs and metabolites were similar. Application of the methods to pharmacokinetic studies of the drugs indicated that they were sufficiently sensitive to measure plasma concentrations for at least three times the elimination half-lives. There was a good correlation between results obtained with the gas chromatographic method and those obtained with the receptor technique. Correlation coefficients were 0.94 (based on 37 samples) for brotizolam and 0.99 (based on on 33 samples) for midazolam, and there were no significant differences between pharmacokinetic parameters obtained with the two methods.(ABSTRACT TRUNCATED AT 250 WORDS)