Dapsone-Induced Methemoglobinemia: Blue Cures Blue

Dapsone, a sulfone group antibiotic, was traditionally used for the treatment of leprosy. It has potent anti-inflammatory and immunosuppressive properties. Hence later, its use has been expanded to conditions such as acne vulgaris, dermatitis herpetiformis, chronic immune thrombocytopenia, pemphigoid, malaria, and cutaneous leishmaniasis. Dapsone is less expensive and effective second-line treatment used in chronic immune thrombocytopenia (c ITP). It is metabolized in the liver by cytochrome P-450 enzymes to potent oxidants that are responsible for the adverse hematological complications like methemoglobinemia. We hereby report a case of dapsone-induced methemoglobinemia in an adult female patient used for the treatment of c ITP. She presented with hypoxia, fatigability, and improved subsequently on low-dose intravenous methylene blue. The patient was discharged without any complications. Initial assessment at Emergency services was suggestive of probable adverse drug reaction according to the WHO causality assessment scale and Naranjo algorithm. The preventability assessment was unpreventable according to Schumock and Thornton preventability assessment scale. A key to the diagnosis of methemoglobinemia is cyanosis with low-oxygen saturation and normal partial pressure of oxygen on arterial blood gas analysis. Treatment should be initiated immediately with IV methylene blue which acts by converting methemoglobin to normal hemoglobin, and thus, increasing the oxygen-carrying capacity of the red blood corpuscles. Dapsone-induced methemoglobinemia is rare but a life-threatening complication. Be cautious, when dapsone is used for the long-term treatment such as c ITP. Relevant pathophysiology and treatment principles are summarized in this case report to enhance awareness among physicians about this life-threatening adverse reaction to dapsone.