Drug-induced methaemoglobinaemia following elective coronary artery bypass grafting

Dapsone can alter the oxygen carrying capacity of haemoglobin. Some patients are more susceptible to these effects because of genetic factors, comorbidities or peri-operative factors such as anaemia. We present a 57-year-old lady who underwent elective coronary artery bypass grafting. Deterioration in neurological and respiratory condition prompted a review of her drug treatment. A combination of long-term dapsone therapy, co-existing cardiac and respiratory disease, postoperative anaemia and renal impairment contributed to her decompensation, despite a relatively low level of methaemoglobin. Successful management included stopping dapsone therapy, supportive care and administration of ascorbic acid.