Kinetics of Distribution of Radioactive Labeled Muscle Relaxants: III. Investigations with 14C‐succinyldicholine and 14C‐succinylmonocholine during Controlled Conditions

A trace dose of 14C-succinylcholine was administered intravenously to dogs under pentobarbital anesthesia and controlled ventilation with air. Five minutes later, 80 per cent of the radioactive material had disappeared from the plasma and 10 per cent was found in the urine. Seven hours later 1.4 per cent of the radioactivity was still present in the plasma, 70 per cent had been eliminated in the urine and 28.6 per cent was untraced. No radioactivity was detected in cerebrospinal fluid.The presence in urine of succinylmonocholine and choline as degradation products was confirmed by radiochromatographic determinations.Pretreatment with hexafluorenium (Mylaxen) slowed the disappearance rate of 14C-succinyldi-choline and its metabolites, and increased urinary elimination.The plasma of the dogs was shown to bind succinyldicholine. The bound fraction gradually increased over five hours to 84 per cent of the total radioactivity (bound and unbound) present in the plasma. Succinylmonocholine also binds to plasma, but to a lesser extent. This correlates well with its more active urinary elimination.