Reminder of important clinical lesson: Acute methaemoglobinaemia after massive nitrobenzene ingestion

Flower-N is a flowering stimulant composition with 22% nitrobenzene. The main systemic effect associated with human exposure to nitrobenzene is methaemoglobinaemia. A 25-year-old female presented after 3 hours following ingestion of 100 ml of 22% Nitrobenzene (Flower-N). Her initial methaemoglobin (MetHb) was 81%; this responded to methylene blue. However, she developed recurrent methaemoglobinaemia on days 3 and 5 with haemolytic anaemia. The treatments that were provided were repeated methylene blue treatment and exchange transfusion. Nitrobenzene ingestion is a known cause of methaemoglobinaemia and haemolytic anaemia. The recurrence suggests a long half-life. The recurrent MetHb has clinical implications as patients may require repeated treatment. Massive nitrobenzene ingestion can cause haemolysis and recurrent methaemoglobinaemia. BACKGROUND Flower-N (Vivid Pesticides, New Delhi) is a flowering stimulant composition with nitrobenzene for agricultural and horticultural flowering crops comprising 22% nitrobenzene as an active ingredient with a natural/synthetic/ionic (or) non-ionic chemical surfactant and a petroleum (or) non-petroleum solvent base. Nitrobenzene toxicity has been well-established in case reports and exposure in man or experimental animals is most often associated with methaemoglobinaemia. Although these reports have been published, there are no previous reports of recurrent methaemoglobinaemia following nitrobenzene ingestion CASE PRESENTATION A 25-year-old previously healthy woman was transferred from a local hospital to the intensive care unit 3 hours after consumption of a whole bottle (100 ml) of Flower-N. She was restless, combative, with obvious cyanosis (fig 1) and a Glasgow Coma Scale (GCS) of 10. There was no jaundice. Pulse was 133 beats/min and blood pressure 100/70 mmHg. Pupils were 3 mm bilaterally with normal reaction. Her respiratory rate was 16 per minute and the rest of her respiratory examination was normal. Bedside pulse oxymetry showed saturation of approximately 84% while she was on 100% oxygen. There were no other significant findings on physical examination INVESTIGATIONS The patient’s blood was noted to be ”chocolate brown” and subsequent arterial blood gas showed a pH 7.447, PaO 61.6, PaCO 28.7, HCO 20, O Sa 92.7% and a methaemoglobin (MetHb) level of 81% (quantitative MetHb level was determined by a method described by Evelyn and Malloy using a visible spectrophotometer ). Initial laboratory findings revealed a haemoglobin level of 14.2 g/dl, white blood count of 14.2×10 /L and showed polymorphonuclear leucocytosis with normal platelet counts and total biliruben. She had mild increase in transaminases (<2-fold). Serum electrolyte levels, urine, electrocardiogram and chest x ray were within normal limits. 1–3 4–8