Further studies on the metabolism of carbidopa, (minus)-L-alpha-hydrazino-3,4-dihydroxy-alpha-methylbenzenepropanoic acid monohydrate, in the human, Rhesus monkey, dog, and rat.

Major urinary metabolites of carbidopa have been identified. Estimates were made based on the recovery or radio activity or by glc analysis of pooled urine of the amounts of the urinary metabolites II (2-methyl-3'-methoxy-4'-hydroxyphenylpropionic acid), III (2-methyl-3,4-dihydroxyphenylpropionic acid), IV (3,4-dihydroxyphenylacetone), V [2-methyl-3-(3'-methoxy-4'-hydroxyphenyl)lactic acid], VI [2-methyl-3-(3',4-dihydroxyphenyl)lactic acid], and VII (3-hydroxy-alpha-methylphenylpropionic acid). Metabolite II represented similar to 10% of the urinary radioactivity in both man and monkey and 16% in the dog. Metabolite III represented 10, 17, and 19% of the urinary radioactivity in man, monkey, and dog. Metabolite IV represented smaller than 5% of the urinary radioactivity in human and dog. Metabolite VII represented similar to 10% of the urinary radioactivity in man and monkey. The corresponding figure for the rat was similar to 20%. In the dog, compounds V and VI represented smaller than 5% of the urinary radioactivity. It was concluded that the loss of the hydrazine functional group(probably as molecular nitrogen) represents the major metabolic pathway for carbidopa.