Acquired methemoglobinemia from phenazopyridine use

Area of Science:

• Pharmacology
• Toxicology
• Internal Medicine

Background:

• Phenazopyridine-induced methemoglobinemia is a rare adverse drug reaction, with fewer than ten cases reported in 35 years.
• This case highlights a unique presentation and initial diagnostic approach to phenazopyridine-induced methemoglobinemia.

Purpose of the Study:

• To report a unique case of phenazopyridine-induced methemoglobinemia.
• To emphasize the importance of considering methemoglobinemia in the differential diagnosis of unexplained hypoxemia.

Main Methods:

• A patient presented with lethargy, diarrhea, light-headedness, and headaches after taking phenazopyridine for dysuria.
• Initial workup revealed persistent hypoxemia, prompting consideration of pulmonary embolism and methemoglobinemia.
• The patient was stabilized, diagnosed, and successfully treated at a main emergency department.

Main Results:

• The patient experienced symptoms including lethargy, diarrhea, light-headedness, and headaches.
• Persistent hypoxemia was observed despite supplemental oxygen.
• Phenazopyridine-induced methemoglobinemia was confirmed and successfully treated.

Conclusions:

• Methemoglobinemia, though rare, can result from over-the-counter medication use and should be included in the differential diagnosis.
• This case underscores the value of comprehensive history taking and physical examination, particularly in resource-limited settings.