Methemoglobinemia from Prolonged Therapeutic Use of Phenazopyridine

Williamson K, Htet N and Nanini S

Department of Emergency Medicine, Advocate Christ Medical Center, USA

^*Correspondance to: Kelly Williamson 

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Abstract:

Background: Phenazopyridine is often prescribed for patients suffering from urinary tract infections as its local analgesic properties can provide immediate symptomatic improvement. It is classically taken for two days while awaiting antibiotic effect. It is available without a prescription in the United States under the trade names: Azo Urinary Pain Relief, Uricalm, and Uristat. Common adverse reactions include urine discoloration, rash, pruritus, nausea, dyspepsia, and headache. Phenazopyridine has been reported to cause methemoglobinemia in overdose, though rarely with therapeutic doses.Case Report: We report a case of an 82-year-old woman who had been taking phenazopyridine at a therapeutic dose for three months when she presented to emergency department with hypoxia. Arterial blood gas revealed a methemoglobinemia level of 15%. Patient’s hypoxia corrected with administration of methylene blue. Why should an emergency physician be aware of this?: Phenazopyridine toxicity, most commonly reported with acute overdose, can lead to methemoglobinemia by converting the iron molecule in hemoglobin to methemoglobin. Administration of methylene blue is typically curative. This case highlights the importance of considering methemoglobinemia in patients who present with hypoxia while taking phenazopyridine.

Keywords:

Methemoglobinemia; Phenazopyridine; Hypoxia; Methylene blue

Cite the Article:

Williamson K, Htet N, Nanini S. Methemoglobinemia from Prolonged Therapeutic Use of Phenazopyridine. Ann Clin Case Rep. 2016; 1: 1085.