S4876 Dapsone-Induced Methemoglobinemia in a Patient With Ulcerative Colitis

Introduction: In patients receiving high doses of corticosteroids and on biologic therapy for inflammatory bowel disease, Pneumocystis jirovecii pneumonia (PJP) prophylaxis with dapsone can be considered. Dapsone-induced methemoglobinemia is a rarely reported complication of dapsone PJP prophylaxis in a patient with inflammatory bowel disease. Case Description/Methods: A 26-year-old White woman with ulcerative pan-colitis who failed tofacitinib, vedolizumab, adalimumab, and ustekinumab status post total colectomy and ileostomy with protectomy was admitted for 1 day history of acute abdominal pain and recurrent hematochezia. Her outpatient medications included upadacitinib 30 mg daily, prednisone 40 mg daily, and dapsone 100 mg daily for PJP prophylaxis. Vitals and labs were notable for persistent tachycardia to 120 beats per minute and C-reactive protein 23.6 mg/dL, erythrocyte sedimentation rate 24 mg/dL, WBC 12.5 k/uL, and hemoglobin 11.8 g/dL. Prednisone and dapsone were continued at home dose. Due to persistent tachycardia and new oxygen requirement of 4-6 L, computed tomography pulmonary embolism was obtained on day 2 of admission. It showed an ill-defined 3 mm ground glass nodule in the right apex. Patient later was found to be positive for COVID and received a 5-day course of remdesivir. Hypoxia improved until day 7 when oxygen requirement rapidly increased to 7 L. Repeat computed tomography pulmonary embolism remained unchanged from prior. Arterial blood gas was without evidence of shunt physiology. Methemoglobin level on day 7 was 8.1%. Dapsone was discontinued immediately. Repeat methemoglobin level the next day was 3.9% with concurrent improvement of oxygen from 7 L to 5 L. Glucose-6-phosphate dehydrogenase deficiency testing showed no evidence of glucose-6-phosphate dehydrogenase deficiency (20.0 U/g Hb). Within 1 week, oxygen requirement returned to room air. She was discharged with prednisone taper 35 mg daily and aerosolized pentamidine for PJP prophylaxis for 4 weeks. Discussion: A rare side effect of dapsone is methemoglobinemia which presents as acutely worsening hypoxemia and dyspnea without evidence of any other cause. A percent methemoglobin greater than thirty percent or greater than twenty percent with worsening hypoxemia are indications for methylene blue. In the current case, methemoglobinemia was diagnosed by identifying rapidly progressing hypoxia in the absence of another etiology in a patient on dapsone prophylaxis for prolonged steroid taper and concurrent Janus Kinase inhibitor use. Other causes of unexplained hypoxia are underlying COVID infection and Janus Kinase inhibitor use; however, she only improved following dapsone discontinuation.