Methemoglobinemia following ingestion of a monolinuron/paraquat herbicide (Gramonol)

A 59-year-old man ingested a mouthful of Gramonol with suicidal intent and was admitted to a local hospital six and a half hours later. It was noted that he looked "ashen grey" and was centrally cyanosed. The methemoglobin and plasma paraquat concentrations performed on arrival at the Regional Poisons Treatment Unit eight hours after paraquat ingestion were 52% and 1100 micrograms/L respectively; the administration of methylene blue reversed methemoglobinemia within two hours. The patient suffered extensive paraquat-induced oral, and probably esophageal, ulceration and developed multiple organ (particularly renal, respiratory and hepatic) failure and died some 10 days later. This is the most severe case of Gramonol poisoning reported both in terms of the amount of paraquat ingested and the concentration of methemoglobin formed. We believe that the methemoglobinemia in this patient was caused by monolinuron not paraquat.