Also, Stages III and IV sleep are decreased. In studies, secobarbital sodium and pentobarbital sodium have been found to lose most of their effectiveness for both inducing and maintaining sleep by the end of 2 weeks of continued drug administration at fixed doses. Therefore, as sleep medications, the barbiturates are of limited value beyond short-term use. Barbiturates have little analgesic action at subanesthetic doses. Rather, in subanesthetic doses these drugs may increase the reaction to painful stimuli.
All barbiturates exhibit anticonvulsant activity in anesthetic doses.
However, of the drugs in this class, only phenobarbital, mephobarbital, and metharbital have been clinically demonstrated to be effective as oral anticonvulsants in subhypnotic doses. Barbiturates are respiratory depressants. The degree of respiratory depression is dependent upon dose. With hypnotic doses, respiratory depression produced by barbiturates is similar to that which occurs during physiologic sleep with slight decrease in blood pressure and heart rate. Studies in laboratory animals have shown that barbiturates cause reduction in the tone and contractility of the uterus , ureters, and urinary bladder.