Identifying the Cause of the "Saturation Gap": Two Cases of Dapsone-induced Methemoglobinemia.

Diaphenylsulfone (DDS: Dapsone) is used for Pneumocystis pneumonia (PCP) prophylaxis, and methemoglobinemia has rarely been reported as a side effect of DDS. We herein report two cases of DDS-related methemoglobinemia in an 81-year-old man with organizing pneumonia and an 84-year-old woman with eosinophilic pneumonia under treatment with prednisolone. Both patients initially received trimethoprim/sulfamethoxazole for PCP prophylaxis and were switched to DDS due to side effects and subsequently exhibited a clinically unexplainable decrease in SpO2. Methemoglobinemia was diagnosed based on the findings of arterial blood gas analyses. In both cases, the methemoglobinemia improved after discontinuing DDS.