THE EXCRETION OF N¹⁵ IN THE URINE OF DOGS AFTER THE ADMINISTRATION OF LABELED PENTOBARBITAL

¹ Department of Pharmacology, College of Physicians and Surgeons, Columbia University, New York; The Research Division of Abbott Laboratories, North Chicago, Illinois

After the oral administration of sodium pentobarbital (Nembutal) labeled with N¹⁵, dogs excreted about 60% of the total dose of excess N¹⁵ in the urine during the first 24 hours. The excess N¹⁵ in the urinary ammonia and urea represented less than 8% of the N¹⁵ so that more than 92% was excreted as pentobarbital or metabolic degradation products derived from the drug. In one isotope-dilution experiment, about 3% of the total excess N¹⁵ in the urine was found to be pentobarbital; this finding confirms the conclusion of other investigators that only minute amounts of pentobarbital are excreted unchanged. Possible structures of the major excretion product or products remain to be considered.