n. an intermediate-acting barbiturate used in the treatment of insomnia and for daytime and preoperative sedation. Like other barbiturates, it is a nonselective CNS depressant and therefore quite toxic in overdose. Because tolerance to its sedative and hypnotic effects accrues much more rapidly than tolerance to its CNS depressant effects, its therapeutic index drops and its potential lethality increases as the dose is increased. These factors, plus its potential for abuse, have caused a decline in its clinical use. U.S. trade name: Butisol Sodium.