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.