Dapsone/sodium-nitroprusside

Abstract

Unmasking of methaemoglobinaemia, which was caused by dapsone: case reportA 58-year-old woman developed methaemoglobinaemia during treatment dapsone, which was unmasked while receiving sodium nitroprusside.The woman, who had anti-phospholipid antibody syndrome presented with gradually worsening breathlessness over 9 months. She was receiving dapsone [route and dosage not stated] along with unspecified oral anticoagulants, azathioprine and prednisolone. Her medical history was significant for acute pulmonary embolism following deep vein thrombosis, and had undergone thrombolysis. She had developed chronic thromboembolic pulmonary hypertension (CTEPH ), causing breathlessness. She also had advanced CTEPH features including right ventricular failure (RVF) and cyanosis. Pulmonary endarterectomy had planned, and while awaiting surgery, she was monitored for oxygen saturation, which displayed between 75% and 90%. She was given supplemental oxygen by facemask when required. She underwent cardiopulmonary bypass (CPB) under anaesthetic induction with fentanyl and pancuronium-bromide. After surgical procedure, cooling was initiated for better visualization of the distal pulmonary arteries, and sodium nitroprusside [dosage not stated] was infused into the CPB circuit for uniform cooling. However, after 20 minutes of CPB, blood in the arterial inflow line appeared to be darker, which was initially thought due to technical failure but later ruled out, and methaemoglobinaemia was unmasked [duration of treatment to reaction onset not stated], which was missed because of cyanosis. Since the darkening of the blood had coincided with hypothermia, rewarming was initiated. And, the colour of arterial blood improved gradually along with the oxygen saturation in the right and left hemispheres. Pulmonary endarterectomy was performed at normothermia with thiopental sodium [thiopentone sodium] administration. The colour of blood became normal at normothermia and with no signs of tissue hypoxia or lactic acidosis. Investigation revealed 9% methaemoglobin in the blood. Finally, it was concluded that the mild methaemoglobinaemia was caused by dapsone therapy, which was unmasked by sodium nitroprusside treatment and hypothermia.The woman had an uneventful post-operative recovery and was discharged 15 days later.