The pharmacokinetics of midazolam in man

Abstract

Midazolam, a new water-soluble benzodiazepine, was administered as: i) 5 mg intravenously, ii) a 10-mg oral solution and iii) a 10-mg oral tablet, to six volunteers whose informed consent had been obtained. Midazolam plasma concentrations were measured using an electron-capture gas-liquid chromatographic assay. After 5-mg intravenous midazolam, subjects fell asleep within 1-2 min and continued to sleep for an average of 1.33 h. After oral midazolam intake (solution or tablets), drowsiness appeared after a average of 0.38 h (range 0.25-0.55 h) and sleep continued for an average of 1.17 h. The time to reach peak plasma midazolam concentration after the 10-mg solution dose (0.37 +/- 0.45 h) did not differ significantly ('t' = 2.04, df = 10, p greater than 0.05) from the time to reach peak plasma midazolam level after the 10-mg tablet dose (0.74 +/- 0.45 h). The terminal half-life, (t 1/2), of midazolam in plasma was 1.77 +/- 0.83 h and there was no significant difference between the mean terminal half-life values obtained for the three midazolam formulations. The mean total clearance (Cl), of midazolam after 5-mg intravenous administration was 0.383 +/- 0.0941 . kg-1 . h-1. The first pass effect, F, determined experimentally (0.36 +/- 0.09) indicated the substantial first pass metabolism of midazolam. The percentage of the midazolam dose excreted unchanged in urine in four subjects during the 0-8-h urine collection interval was very small (0.011%-0.028%).