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To predict drug interactions with estazolam, the biotransformation of estazolam to its major hydoxylated metabolite, 4-hydroxyestazolam was studied in vitro using pooled human liver microsomes and individual expressed human cytochrome P450 (CYP) enzymes. Estazolam was metabolized to 4-hydroxyestazolam according to the Hill kinetic model in pooled human liver microsomes. The K m value for the 4-hydroxylation of estazolam was 24.1?µM, and the V max value was 52.6?pmol?min -1 ?mg -1 protein. The formation of 4-hydroxyestazolam from estazolam in pooled human liver microsomes was significantly inhibited by itraconazole and erythromycin, specific CYP3A4 inhibitors, in a dose-dependent manner, with IC50 values of 1.1 and 12.8?µM, respectively. When estazolam was incubated with expressed human CYP enzymes (CYP1A2, CYP2A6, CYP2C9, CYP2C19, CYP2D6, CYP2E1 and CYP3A4), it was metabolized only by CYP3A4. In conclusion, the biotransformation of estazolam to 4-hydroxyestazolam was catalyzed by CYP3A4. [ABSTRACT FROM AUTHOR]

Objective: To examine the effect of carbamazepine on the single oral dose pharmacokinetics of etizolam. Methods: Eleven healthy male volunteers received carbamazepine 200 mg/day or placebo for 6 days in a double-blind, randomized, crossover manner, and on the sixth day they received a single oral 1-mg dose of etizolam. Blood samplings and evaluation of psychomotor function by the Digit Symbol Substitution Test and Stanford Sleepiness Scale were conducted up to 24 h after etizolam dosing. Plasma concentration of etizolam was measured using high-performance liquid chromatography. Results: Carbamazepine treatment significantly decreased the peak plasma concentration (17.5±4.1 ng/ml versus 13.9±4.1 ng/ml; P<0.05), total area under the plasma concentration-time curve (194.8±88.9 ng h/ml versus 105.9±33.0 ng h/ml; P<0.001), and elimination half-life (11.1±4.6 h versus 6.8±2.8 h; P<0.01) of etizolam. No significant change was induced by carbamazepine in the two pharmacodynamic parameters. Conclusions: The present study suggests that carbamazepine induces the metabolism of etizolam. [ABSTRACT FROM AUTHOR]

Objective. To clarify the involvement of cytochrome P450 (CYP) 3A4 in the metabolism of etizolam. Methods. The effects of itraconazole, a potent and specific inhibitor of CYP3A4, on the single oral dose pharmacokinetics and pharmacodynamics of etizolam were examined. Twelve healthy male volunteers received itraconazole (200 mg/day) or placebo for 7 days in a double-blind randomized crossover manner, and on the 6th day they received a single oral 1-mg dose of etizolam. Blood samplings and evaluation of psychomotor function using the Digit Symbol Substitution Test and Stanford Sleepiness Scale were conducted up to 24 h after etizolam dosing. Plasma concentration of etizolam was measured by means of high-performance liquid chromatography. Results. Itraconazole treatment significantly increased the total area under the plasma concentration–time curve (AUC; 213±106 ng⁃h/ml versus 326±166 ng⁃h/ml, P<0.001) and the elimination half-life (12.0±5.4 h versus 17.3±7.4 h, P<0.01) of etizolam. The 90% confidence interval of the itraconazole/placebo ratio of the total AUC was 1.38–1.68, indicating a significant effect of itraconazole. No significant change was induced by itraconazole in the two pharmacodynamic parameters. Conclusion. The present study suggests that itraconazole inhibits the metabolism of etizolam, providing evidence that CYP3A4 is at least partly involved in etizolam metabolism. [ABSTRACT FROM AUTHOR]