Acquired methemoglobinemia from phenazopyridine use

BACKGROUND: Phenazopyridine-induced methemoglobinemia is relatively rare with fewer than ten cases reported over the past 35 years. We describe a case of phenazopyridine-induced methemoglobinemia that is unique in the way the patient presented and how initial workup was completed. CASE PRESENTATION: The patient presented with lethargy, diarrhea, light-headedness, and headaches, with past medical history of breast cancer, seizures, and recent dysuria for which she had been taking phenazopyridine. She was noted to have a persistent hypoxemia despite supplemental oxygen delivery and a shunting process was considered, with pulmonary embolus and methemoglobinemia due to phenazopyridine use being of chief concern. She was stabilized, and confirmation of original diagnosis was made at the main ED and treatment successfully rendered with good effect. CONCLUSIONS: Methemoglobinemia, while rare, can be associated with use of over-the-counter medicines and should be considered as part of a broad differential. This case serves to emphasize the importance of a thorough history and physical—tools especially helpful when at a satellite facility with relatively limited resources.