A Case of Severe Hypoxia Caused by Phenazopyridine-Induced Methemoglobinemia: A near Fatal Event from Over-the-Counter Medication Use

Abstract

Methemoglobinemia is a rare blood disorder characterized by the oxidation of heme iron from ferrous (Fe2+) to ferric (Fe3+) state, which increases oxygen affinity and impairs oxygen release to the tissue causing hypoxia. It can be congenital or acquired; however, most cases are acquired and caused by exogenous substances such as medications, chemicals, and environmental substances. Phenazopyridine is an over-the-counter urinary analgesic medication commonly used for symptomatic relief of dysuria and has been reported to cause methemoglobinemia. However, only a handful of cases of phenazopyridine-induced methemoglobinemia have been reported. We present a case of an 89-year-old female who presented with severe hypoxia, shortness of breath, headache, nausea, and dizziness caused by phenazopyridine-induced methemoglobinemia. She was found to have a methemoglobin level of 21.5% and was treated with methylene blue, leading to a rapid improvement of her symptoms. She was taking one over-the-counter phenazopyridine 200 mg tablet three times daily for two weeks for her chronic dysuria. This case highlights the need to have a high index of suspicion of phenazopyridine-induced methemoglobinemia in a patient presenting with unexplained shortness of breath with a history of phenazopyridine use as it could lead to severe methemoglobinemia with hypoxia that could potentially be fatal if not promptly diagnosed.

Phenazopyridine-Induced Methemoglobinemia in a Jehovah’s Witness Treated with High-Dose Ascorbic Acid Due to Methylene Blue Contradictions: A Case Report and Review of the Literature

“…Over-the-counter in the United States, the maximum dose obtainable is 199 mg per dose. It has been noted as the cause of methemoglobinemia in a few case reports [ 7 , 8 , 9 , 10 , 11 , 12 , 13 ]. In most cases in the current literature, patients were taking the drug either for an extended period of time beyond the recommended two days or at a larger dosages than the recommended daily dose.…”