A bioassay for a water-soluble benzodiazepine against sodium thiopental

The authors performed a bioassay of midazolam maleate, an investigational, water-soluble benzodiazepine; to determine the duration of sleep after a single intravenous dose. Sodium thiopental was the standard against which the midazolam maleate was assayed. Prior to operation 60 surgical patients were randomly given one of five doses of drugs, either thiopental, 180 or 270 mg, or midazolam maleate, 6.6, 10, or 15 mg. The designated drug was infused intravenously over 20 sec in a double-blind fashion. Sleep was defined as commencing when the patients stopped counting, and ending when they could respond appropriately to verbal commands. Midazolam maleate, 10 mg (9--12 mg represents 95 per cent confidence limits), was found to be equivalent to thiopental, 200 mg, in the duration of sleep induced. Apnea following the infusion was less frequent and of shorter duration after midazolam maleate than after thiopental. It is concluded that midazolam maleate is a satisfactory agent for the induction of anesthesia, and that it is about 20 times as potent as thiopental.