SPL Set ID: 5d1f0f48-06d9-4408-b9a2-60d7a09d942f

The barbiturates are nonselective central nervous system (CNS) depressants that are primarily used as sedative-hypnotics. In sub-hypnotic doses, they are also used as anticonvulsants. The barbiturates and their sodium salts are subject to control under the Federal Controlled Substances Act. Phenobarbital is a barbituric acid derivative and occurs as white, odorless, small crystals or crystalline powder that is very slightly soluble in water; soluble in alcohol, in ether, and in solutions of fixed alkali hydroxides and carbonates; sparingly soluble in chloroform. Phenobarbital is 5-ethyl-5-phenylbarbituric acid. Phenobarbital is a substituted pyrimidine derivative in which the basic structure is barbituric acid, a substance that has no CNS activity. CNS activity is obtained by substituting alkyl, alkenyl, or aryl groups on the pyrimidine ring. It has the following structural formula: Each phenobarbital tablet contains 16.2 mg, 32.4 mg, 64.8 mg, or 97.2 mg of phenobarbital, USP. Phenobarbital Tablets USP Structural Formula