Central-nervous-system toxicity of local anesthetic mixtures in monkeys

The central-nervous-system toxicities of local anesthetic mixtures consisting of lidocaine and etidocaine or lidocaine and tetracaine, administered intravenously to four healthy, non-medicated rhesus monkeys, were evaluated. Toxicities were compared by determining seizure dosages for each drug alone and then in a lidocaine-etidocaine-tetracaine mixture. Arterial plasma levels of lidocaine and etidocaine at which electrical seizure activity occurred also were measured when the drugs were administered alone and in combination. The seizure dosages and arterial plasma levels for the drug mixtures studied were equal to the sums of the dosages and thresholds for individual constituents of the mixtures. Under the conditions of this investigation local anesthetic toxicity was additive. (Key words: Anesthetics, local, lidocaine; Anesthetics, local, etidocaine; Anesthetics, local, tetracaine; Brain, seizure thresholds; Toxicity, convulsions.)