SummaryMidazolam (MDZ) is metabolized by CYP3A. Glucocorticoids are potent inducers of CYP3A in humans. The possible interaction between intravenous MDZ and chronically administered glucocorticoids was investigated during surgery in patients. MDZ (0.2 mg/kg) was administered intravenously to 8 patients taking glucocorticoid chronically and 10 patients not taking glucocorticoid. In patients taking glucocorticoid, the AUC0-∞and CL of MDZ was decreased to 63.9% (16.3 ± 10.5 vs 25.5 ± 20.7 &mgr;g × min/mL) and increased to 127.5% (16.7 ± 10.7 vs 13.1 ± 8.3 mL/min/kg) of that in the control group, respectively. The terminal t½values of MDZ were similar in two groups. In patients taking glucocorticoid, the AUC0-∞of 1´-hydroxymidazolam (1´-OH MDZ) was 66.7% of that in the control group (7.6 ± 2.6 vs 11.4 ± 9.7 &mgr;g × min/mL), and the terminal t½of 1´-OH MDZ was significantly (p< 0.01) decreased (1.8 ± 0.5 vs 3.0 ± 0.8 hr). Accumulative urinary excretion of 1´-OH MDZ glucuronide was increased to 157.6%. These observations might be results from induction of CYP3A4 and/or UDP-glucuronosyltransferase by glucocorticoids.