Metabolic disposition of [14C] metanil yellow in rats

The absorption, metabolism and excretion of [14C] metanil yellow was studied in rats. Following administration of a single oral dose of 5 mg dye (7.6 microCi)/kg body weight, 80.5% of the dose was excreted in the urine and faeces within 96 hr, with the majority being accounted for in the faeces. Liver, kidney, spleen and testis retained no count whereas 13.6% of the radioactivity was retained by gastrointestinal tract. Analysis of urine and faeces detected two azo-reduction metabolites of metanil yellow which were characterized by TLC and IR, NMR and mass spectroscopic studies as metanilic acid and p-aminodiphenylamine.