Pentobarbital and thiopental anesthetic interactions with midazolam.

The effects of midazolam-pentobarbital and midazolam-thiopental combinations on the righting reflex were studied in rats. Doses that block the righting reflex for the agents given alone and for their combinations were determined with a probit procedure and compared with an isobolographic analysis. Interactions between pentobarbital or thiopental and midazolam were found to be synergistic (supra-additive). The degree of synergism was almost identical with both combinations. The ability of barbiturates to increase the affinity of benzodiazepine receptors to midazolam may be the underlying mechanism for the observed synergism.