Dapsone is used in the treatment of a variety of dermatological conditions and prophylaxis of
opportunistic infections. However, if consumed at a dose of more than 200 mg/day, it can cause
methemoglobinemia, a condition characterized by elevated methemoglobin levels in the blood;
methemoglobin is an abnormal form of
hemoglobin, containing
iron in the ferric state (Fe3 +) rather than the reduced ferrous form (Fe2 +) found in
hemoglobin. A small amount of it is produced in the body due to
oxidant damage to the red blood cells.
Methemoglobinemia can cause varied clinical manifestations involving the cardio-respiratory and nervous systems depending upon the level of
methemoglobin. While it could be congenital, it is commonly caused by exposure to drugs that cause oxidation of
hemoglobin, such as
benzocaine,
dapsone, and
nitrates. We report a case of
dapsone-induced
methemoglobinemia in a previously healthy young female who had consumed 15
tablets of
dapsone 100 mg with suicidal intent. She presented with central
cyanosis,
breathlessness, and altered sensorium after five days of consumption. While the pulse-oximeter showed oxygen saturation (SaO2) of 84%, arterial blood gas (ABG) analysis showed partial pressure of
oxygen (PaO2) of 427 mmHg and SaO2 of 98%. This "saturation gap" occurred due to the presence of the abnormal
hemoglobin variant. Her
cyanosis did not improve despite giving 100% supplemental
oxygen. There was no cardiac or respiratory cause to account for her
cyanosis. Her
methemoglobin level was 45.8%. She was successfully treated with specific
antidote methylene blue,
mechanical ventilation, and other symptomatic measures. The purpose of this presentation is to help clinicians recognize this condition early, because, if left untreated, it might prove fatal. The diagnostic clues include refractory
hypoxemia, central
cyanosis in the absence of cardiac and respiratory causes, saturation gap, and chocolate-colored blood.