PROTRACTED METHEMOGLOBINEMIA AFTER PHENAZOPYRIDINE OVERDOSE IN AN INFANT

Acquired methemoglobinemia may be produced by the ingestion or absorpt ion of certain chemicals and xenobiotics. A case of methemoglobinemia in an 8.5-month old infant who ingested approximately 227 mg/kg of phe nazopyridine is presented, Although this adverse event is often revers ed with a single dose of methylene blue, this patient required three d oses of methylene blue (1 mg/kg) over a 25-hour period. It is suggeste d that the need for repeated doses of methylene blue in this case was not only related to the large dose of phenazopyridine, but also its me tabolites (i.e., aniline), which have the potential to produce methemo globinemia. This case illustrates the need for close observation and s erial monitoring of methemoglobin levels in patients who are at increa sed risk for the development of protracted methemoglobinemia. Integrat ion of knowledge of developmental pharmacology, drug metabolism, and p harmacodynamic properties are critical determinants in the evaluation and treatment of patients with drug-induced methemoglobinemia.