Excretion and Biotransformation of Carboxymethyl-cysteine in Rat, Dog, Monkey and Man

1. Following an oral dose of S-carboxymethyl [35S]cysteine monkey (rhesus and African green), rat, dog, and man excreted 77,88,95, and 100% respectively of the 35S radioactivity in urine and 7.0, 2.5, 0.7, and 0.3% in faeces during a 3 to 4 day period. 2. The principal drug-related components excreted were unchanged carboxymethylcysteine, dicarboxymethyl sulphide and inorganic sulphate. 3. Rat, dog, and man excreted primarily dicarboxymethyl sulphide and unchanged carboxymethylcysteine and no inorganic sulphate (rat, 7%). 4. Monkey excreted largely inorganic sulphate, moderate amounts of dicarboxymethyl sulphide and a trace of unchanged drug.