Preliminary Evaluation of the Efficacy and Safety of Brimonidine for General Anesthesia

Background: To determine the hypnotic and analgesic effects of brimonidine, and evaluate its efficacy and safety for general anesthesia. Potentiation of pentobarbital sleeping time with brimonidine was observed in mice, as was analgesic activity of brimonidine. Methods: : The median effective dose (ED 50 )and lethal dose (LD 50 ) of intraperitoneally injected brimonidine were determined in hypnotized mice. In addition, LD 50 of intravenously injected brimonidine, ED 50 of intravenously , intramuscularly and intrarectally injected brimonidine in hypnotized rabbits were determined. The synergistic anesthetic effect of brimonidine and chloral hydrate on rabbits was evaluated. Results: : Intraperitoneal injection of 10 mg/kg brimonidine enhanced the hypnotic effect of a threshold dose of pentobarbital. Intraperitoneal injection brimonidine produced dose-related analgesic effects in mice. ED 50 of intraperitoneally administered brimonidine in hypnotized mice was 75.7 mg/kg, and LD 50 was 379 mg/kg. The ED 50 of intravenous, intramuscular and intrarectal brimonidine for hypnosis in rabbits were 5.2 mg/kg, 8.8 mg/kg and 8.7mg/kg, respectively, and LD 50 of intravenous brimonidine was 146 mg/kg. Combined intravenous administration of 0.6 mg/kg brimonidine and 0.03 g/kg chloral hydrate had a synergistic anesthetic effects. Conclusions: : Brimonidine elicited hypnotic and analgesic effects after systemic administration, and exhibited safety. Brimonidine enhanced the effects of other types of narcotics when combined.