SHM Converge Scientific Abstract ePoster Gallery-Triple Threat: Sulfa Allergy, Dapsone-Induced Methemoglobinemia and Atovaquone-Associated Anemia

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This case describes a 68-year-old woman with small cell neuroendocrine lung cancer who needed Pneumocystis jirovecii pneumonia (PCP) prophylaxis because of long-term prednisone use. Because of a sulfa allergy, she was started on dapsone after normal CBC, liver tests, and G6PD levels.<br /><br />Three days later, she returned with dyspnea, lightheadedness, and hypoxia. Workup was unrevealing, but arterial blood gas with co-oximetry showed methemoglobinemia, including a “saturation gap” and chocolate-brown blood. Dapsone was stopped and replaced with atovaquone, and her respiratory status improved.<br /><br />However, three weeks after discharge, she developed fatigue, exertional dyspnea, palpitations, and lightheadedness. She was found to have hypoproliferative macrocytic anemia with hemoglobin 9.5 g/dL. Extensive evaluation did not identify another cause. Atovaquone was discontinued, and the anemia resolved spontaneously.<br /><br />The report emphasizes several teaching points:<br />- TMP-SMX is the preferred PCP prophylaxis, but dapsone and atovaquone are common alternatives when sulfa drugs cannot be used.<br />- Dapsone can cause methemoglobinemia even at prophylactic doses and even without G6PD deficiency.<br />- Methemoglobinemia should be suspected when hypoxia does not correct as expected, especially with cyanosis, dyspnea, and a saturation gap.<br />- Management includes stopping the offending drug, oxygen support, and sometimes methylene blue or ascorbic acid.<br />- Atovaquone can rarely cause cytopenias, including anemia, so blood count monitoring is important.<br /><br />Overall, the case highlights the need to recognize uncommon but serious hematologic adverse effects of PCP prophylaxis alternatives.

Asset Subtitle

Yu-Han Chen

Meta Tag

Author List Chadane Thompson, Dipal R. Patel, Shalva Eliava, Smitha Agadi, Yu-Han Chen

Category Clinical Vignettes

Concept Trimethoprim-sulfamethoxazole

Concept Dapsone

Concept Methemoglobinemia

Concept Pneumocystis Pneumonia Prophylaxis

Concept Atovaquone

Distinguished Non-Finalist

Presenter Organization Department of Internal Medicine, Englewood Hospital and Medical Center

Presenting Author Yu-Han Chen

Track Adult

Keywords

Pneumocystis jirovecii pneumonia

PCP prophylaxis

dapsone

methemoglobinemia

saturation gap

atovaquone

macrocytic anemia

sulfa allergy

G6PD deficiency

hematologic adverse effects

Trimethoprim-sulfamethoxazole

Dapsone

Methemoglobinemia

Pneumocystis Pneumonia Prophylaxis

Atovaquone