DAPSONE-INDUCED METHEMOGLOBINEMIA TREATED WITH ORAL CIMETIDINE: A CASE REPORT

Abstract

SESSION TITLE: Tuesday Medical Student/Resident Case Report Posters SESSION TYPE: Med Student/Res Case Rep Postr PRESENTED ON: 10/22/2019 01:00 PM - 02:00 PM INTRODUCTION: Dapsone is an antibiotic with anti-inflammatory properties commonly utilized in the treatment of various immunologic skin disorders. It is known to cause methemoglobinemia, a functional anemia characterized by an increased level of methemoglobin resulting in impaired oxygen release to tissues. We report a case of dapsone-induced methemoglobinemia successfully managed with oral cimetidine. CASE PRESENTATION: A 72-year-old male presented to the emergency department with the complaint of sudden onset of shortness of breath after undergoing a cardiac ablation three days prior to presentation. His past medical history included atrial fibrillation, cardiomyopathy, and an inflammatory skin condition known as granuloma annulare (GA). Of note, he was started on dapsone 100 mg daily for GA about a week prior to presentation. Pulse oximetry on admission demonstrated an oxygen saturation of 81 percent on room air despite the arterial blood gas (ABG) demonstrating a partial pressure of oxygen of 134 mm Hg. The patient’s methemoglobin level was noted to be elevated at 7.2 percent. Physical examination revealed crackles in bilateral lung flies. In addition, interstitial pulmonary edema was demonstrated on chest X-ray. The patient was admitted and treated for heart failure with furosemide. His home medications including dapsone were continued. On hospital day two, despite showing improvement in his pulmonary edema, the patient continued to require 12 liters of oxygen to maintain an adequate oxygen saturation. On hospital day 3, a repeat ABG revealed an increase in methemoglobin levels to 14.2 percent . Given these findings, dapsone-induced methemoglobinemia was suspected. Dapsone was discontinued and oral cimetidine 400 mg three times daily was initiated. About 22 hours after cimetidine was administered, methemoglobin level decreased to 5.5 percent. Methemoglobin continued to drop to 4.9 another 24 hours later. On hospital day six, the patient’s shortness of breath had completely resolved and his oxygen saturation improved to 95 percent on room air. No side effects to cimetidine were noted. The patient was discharged to home and prescribed cimetidine to be continued for one more week after discharge. DISCUSSION: Cimetidine, a histamine-2 receptor antagonist, can mitigate dapsone-induced methemoglobinemia by inhibiting the cytochrome P450 metabolism of dapsone to its toxic hydroxylamine metabolites, which are believed to be the cause of methemoglobinemia. Cimetidine can be given to prevent the further production of methemoglobin and thus further toxicity from dapsone. In this patient, a significant decrease in methemoglobin level and clinical improvement were observed within 24 hours of initiating cimetidine. CONCLUSIONS: This case provided evidence that oral cimetidine with discontinuation of dapsone may be an effective and well-tolerated option for the acute treatment of dapsone-induced methemoglobinemia. Reference #1: Ashurst JV, et al. Pathophysiologic mechanisms, diagnosis, and management of dapsone-induced methemoglobinemia. J Am Osteopath Assoc. 2010 Jan;110(1):16-20. Reference #2: Malfara WR. Effects of H(2)-receptor antagonists on dapsone-induced methaemoglobinaemia in rats. Pharmacol Res. 2002 Apr;45(4):269-73. Reference #3: Burke P, et al. Dapsone-induced methemoglobinemia: case of the blue lady. Can Fam Physician. 2013 Sep;59(9):958-61. DISCLOSURES: Speaker/Speaker's Bureau relationship with Allergan Please note: $5001 - $20000 Added 03/20/2019 by Frances Loftus, source=Web Response, value=Honoraria Speaker/Speaker's Bureau relationship with Boerhyinger ingelheim Please note: $1001 - $5000 Added 03/20/2019 by Frances Loftus, source=Web Response, value=Honoraria No relevant relationships by Natalie Millet, source=Web Response Speaker/Speaker's Bureau relationship with Melinta Pharmaceutical Please note: $1001 - $5000 Added 03/18/2019 by Joseph Reilly, source=Web Response, value=Honoraria