Isolation and identification of two hydroxylated metabolites of phenazopyridine in rat urine.

Together with the metabolites arised from the reductive cleavage of the azo linkage, two hydroxylated metabolites of phenazopyridine (2,6-diamino-3-[(4-hydroxyphenyl)azo]pyridine and and 2,6-diamino-3-[(2-hydroxyphenyl)azo]pyridine) were identified in rat urine, after the administration of 50 mg/kg of the drug. The structures of these metabolites were elucidated, after TLC separation, by means of I.R., N.M.R. and mass spectrometry. The presence of two hydroxylated metabolites of the intact drug support evidence that phenazopyridine is also subjected in vivo to oxidative metabolism.