The paramedics found the patient somnolent with systolic blood pressure 110 mm Hg, heart rate 130 bpm, oxygen saturation 79% with notable cyanosis and diaphoresis. Sodium nitrite is commonly used in food preservation and in treating cyanide toxicity. Despite this, the diagnosis is clear when considering the initial patient report of sodium nitrite ingestion, his clinical presentation, profound acidaemia and nitrite test results.4 Methylene blue is the mainstay of treatment for methaemoglobinemia and is dosed 1–2 mg/kg, infused over 5 min and can be repeated if symptoms persist.1 Methylene blue is a catalyst for reducing methaemoglobin to haemoglobin within erythrocytes, via the enzyme NADPH-methaemoglobin reductase (figure 3).2 Additional treatment approaches include ascorbic acid, hyperbaric oxygen, exchange transfusion and extracorporeal membrane oxygenation.3 5 Figure 3.