Anesthetic interaction between midazolam and halothane in humans.

The present study was undertaken in humans to determine the anesthetic efficacy of midazolam in terms of its ability to reduce halothane minimum alveolar anesthetic concentration (MAC). Fifty women scheduled for simple or radical hysterectomy were allocated randomly to one of four groups; group A was given no midazolam as a control; groups B, C, and D were given midazolam intravenously by a bolus of 0.1, 0.2, and 0.4 mg/kg followed by infusion of 1, 2, and 4 micrograms.kg-1 x min-1, respectively. Halothane MAC was 0.78%, 0.47%, 0.38%, and 0.23% at mean serum midazolam concentrations of 0, 134, 250, and 539 ng/mL in groups A, B, C, and D, respectively. The interaction between halothane and midazolam in the anesthetic efficacy conformed to an exponential fit. The results indicate that midazolam produces marked reduction of halothane MAC in humans at serum concentrations lower than that required to cause sleep. Lastly, midazolam's potentiation of halothane has a saturated nature.