Phenazopyridine is metabolized to this metabolite that is presumed to play a contributory role for persistent, recurring methemoglobinemia after large doses of phenazopyridine.
Aniline. After therapeutic doses, approximately 8% of phenazopyridine is metabolized to aniline. However, in overdoses, these authors theorize that this percentage is higher and may be contributing to persistent, recurrent methemoglobinemia.
Christensen CM et al. Protracted methemoglobinemia after phenazopyridine overdose in an infant. J Clin Pharmacol 1996; 36: 112-116. https://accp1.onlinelibrary.wiley.com/doi/epdf/10.1002/j.1552-4604.1996.tb04175.x