(2R)-3-(3,4-dihydroxyphenyl)-2-hydrazinyl-2-methylpropanoic acid; α-Hydrazino-3,4-dihydroxy-α-methyl-benzenepropanoic Acid; Carbidopa Monohydrate - Impurity K (EP/BP) (As per EP Monograph 37.1); (R)-3-(3,4-Dihydroxyphenyl)-2-hydrazinyl-2-methylpropanoic acid; R-(+)-Carbidopa