• I Kissin, H R Vinik, and E L Bradley.
• Department of Anesthesiology, School of Medicine, University of Alabama, Birmingham 35294.
• J Clin Anesth. 1991 Sep 1; 3 (5): 367-70.

Study ObjectiveTo test the hypothesis that midazolam potentiates thiopental sodium-induced unconsciousness.DesignRandomized, double-blind study.SettingA university medical center.PatientsFifty nonpremedicated ASA physical status I and II adult patients scheduled for eye surgery.InterventionsIntravenous (IV) injections of thiopental sodium in doses ranging from 1.0 mg/kg to 4 mg/kg with or without the addition of midazolam 0.02 mg/kg.Measurements And Main ResultsInability to open eyes on command was used as an end point of anesthesia and the dose-response curves were determined using a probit procedure. A dose of 0.02 mg/kg, which constitutes less than one-tenth of the hypnotic ED50 value for midazolam, potentiated thiopental sodium anesthesia. The thiopental sodium ED50 value was decreased from 2.4 mg/kg to 1.6 mg/kg (p less than 0.001). Midazolam also reduced individual variability in the response to thiopental sodium. As a result, the thiopental sodium dose that reliably induced any nonpremedicated patient decreased from 6 mg/kg (ED99 of 5.57 mg/kg) to 2.5 mg/kg (ED99 of 2.37 mg/kg).ConclusionsA subhypnotic dose of midazolam potentiates thiopental sodium-induced unconsciousness. This effect suggests the possibility that midazolam enhances barbiturate binding.

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