Treatment of Dapsone-Induced Methemoglobinemia in a Transplant Recipient With Isosulfan Blue Allergy

Dapsone is often used for Pneumocystis jirovecii pneumonia prophylaxis in post-transplant patients when sulfamethoxazole/trimethoprim is not tolerated. Methemoglobinemia (MetHb) is a known side effect of dapsone, frequently treated with methylene blue. We describe unexplained hypoxemia in a post-transplant patient on dapsone, highlighting the need for a high index of suspicion to recognize and manage this disorder. In this case, cimetidine was used to successfully treat MetHb when methylene blue was unsafe due to an isosulfan blue allergy. This suggests cimetidine may be a safe, effective alternative for acute symptomatic dapsone-induced MetHb in high-risk patients.