Printed in U. S. A. THE METABOLISM AND ELIMINATION OF S-CARBOXYMETHYL-L-CYSTEINE IN MAN

The metabolism of 14C- and 35S-labeled S-carboxymethylcysteine (SCMC) has been compared. The majority of the dose appeared in urine in the first 24 hr; no activity was detectable in feces. Use of 35S-Iabeled compound gave small amounts of inorganic 35S-sulfate, whereas 14C-labeled material was degraded to give some (14C]urea. Peak excretion of the parent compound occurred first after admin-istration of SCMC; metabolites requiring one chemical modification for their formation were maximally excreted 1-4 hr after the dose and those involving more metabolic processes appeared later (4-8 hr). S-Carboxymethyl-L-cysteine 13-(S-carboxymethylthio)alanine] is a mucolytic agent presently being used in Europe as supportive therapy in the treatment of respiratory disorders. Investigations have shown that it is extensively metabolized in man, as well as the rat, rabbit, guinea-pig, dog, marmoset, rhesus monkey, an