Phenazopyridine-induced sulfhemoglobinemia: A diagnostic and management dilemma
Files
Publication Date
4-29-2026
Keywords
oregon, psvmc, psvmc gme, psvmc oaa
Disciplines
Medical Education
Abstract
Introduction: Sulfhemoglobinemia is a rare dyshemoglobinemia which occurs when sulfur irreversibly binds to hemoglobin. Presents similarly to methemoglobinemia. Common offending medications: dapsone, acetanilide, phenacetin, and nitrates. Rarely observed secondary to phenazopyridine, an over-the counter medication used to treat dysuria. Few facilities are capable of testing for sulfhemoglobinemia Case Background: A 67-year-old woman with recurrent urinary tract infections and interstitial cystitis presented with encephalopathy and recurrent falls for three days. PMH: multiple sclerosis, recurrent urinary tract infections, asthma, neurogenic bladder, neuropathic pain, and obstructive sleep apnea. Chronically on multiple centrally acting medications. Not on medications for multiple sclerosis due to cost. Has many urinary tract infections annually Usually infected with antibiotic resistant bacteria, including escheria coli, raoultella ornithinolytica, and klebsiella pneumoniae. Often requires meropenem to treat for infections given degree of resistance. Per husband, chronically takes large doses of phenoazopyridine (available over the counter as Azo) to treat her interstitial cystitis Dosage: Recommended: no more than 2 days without consulting doctors Actual: multiple bottles of Azo weekly Conclusion: 1. Sulfhemoglobinemia is rare & difficult to diagnose, unlike ethemoglobinemia which is uncommon but easily identified & diagnosed 2. Common causes of sulhemoglobinemia: medications, including over-the counter drugs such as phenazopyridine 3. Rapid identification of the uncommon conditions are key in managing patients with one or both of these dyshemoglobinemias
Specialty/Research Institute
Graduate Medical Education
Specialty/Research Institute
Internal Medicine
