Abstract

A radioimmunoassay is described in which levels as low as 500 pg of various barbiturates can be detected. The assay method is applicable to the determination of barbiturate levels in plasma, urine on brain homogenates. With this technique, the plasma level of pentobarbital in the rat had a T_1/2 of 1.7 hours and barbital a T_1/2 of 19.3 hours. The specificity of the antibodies requires a 6-membered ring with an intact urea portion, as well as a cambonyl grouping at positions 4 and 6 on the ring. However, a variety of substitu ents at carbon 5 are allowed without destroying the ability to be recognized by the antibody.