Anesthetic drug interaction: an overview.

Modern anesthetic techniques involve combinations of intravenous (i.v.) and inhaled anesthetic drugs that may produce synergistic (supraadditive), additive, or antagonistic interactions. Synergistic interaction is most likely to occur when two or more drugs produce similar effects by different mechanisms. All of the tested combinations of opioids and i.v. sedative-hypnotics have been shown to produce synergistic hypnotic effects, and the majority of these interactions are predictable and useful in daily practice. Opioids, benzodiazepines, lidocaine, and alpha-2 agonists can all reduce the requirements for volatile anesthetics, but only the opioids and the alpha-2 agonists produce this effect at clinically acceptable concentrations. The usefulness of a drug interaction depends on whether it produces greater efficacy or reduced toxicity. Surprisingly, these outcomes have only been specifically measured for a handful of common drug combinations.