Midazolam acts synergistically with methohexitone for induction of anaesthesia.

The induction dose-response of midazolam was compared with the dose-response of its combination with methohexitone sodium and with that of methohexitone alone. Three groups of 60 unpremedicated ASA physical state I or II women undergoing minor gynaecological interventions were studied. The end-point of induction of anaesthesia was inability to open eyes upon command. Dose-response curves were determined for each group with a probit procedure and compared with an isobolographic analysis. Midazolam was found to act in synergism with methohexitone for induction of anaesthesia. Twenty-seven percent ED50 for methohexitone was required in combination with 33% of ED50 for midazolam to achieve the ED50 of the combination. This degree of synergism is in agreement with that described in animal research.