Phenazopyridine-Induced Methemoglobinemia: A Case Report

Abstract

Methemoglobinemia is a condition caused by increased methemoglobin, a reduced form of hemoglobin, in the blood. This causes the molecules to bind oxygen more tightly and decreases their ability to release that oxygen to tissue. Most cases of methemoglobinemia are acquired and occur either in pediatric populations or in individuals with predisposing conditions. This report illustrates a case of an otherwise healthy 31-year-old patient presenting to the emergency department with cyanosis of the hands and mouth and an O2 saturation of 78% after taking increased doses of the over-the-counter medication phenazopyridine. A "chocolate-brown" color of her arterial blood, and increased methemoglobin levels of 20.2%, confirmed the diagnosis of methemoglobinemia. She was treated with both methylene blue and ascorbic acid, and her oxygen saturation and serum chemistry returned to normal levels within a few hours. The case highlights the importance of discussing the dosage of all over-the-counter medications with patients and recognizing the signs and symptoms of methemoglobinemia.

Keywords: acquired methemoglobinemia; arterial blood gas; case report; methylene blue; phenazopyridine; toxicology; urinary tract infection.