Superwarfarin poisoning

Abstract

A 36-year-old female presented to hospital with a significantly elevated international normalised ratio (INR). In the following days, her INR continued to fluctuate after repeated doses of parenteral phytomenadione (vitamin K 1), fresh frozen plasma and Prothrombinex (human coagulation factors II, IX and X). The patient denied taking warfarin, which was confirmed by a standard plasma warfarin assay. A range of tests were performed and 18 days after admission, brodifacoum was isolated from her blood. Brodifacoum is the commonest type of 'superwarfarin'; a rodenticide developed in the 1970s to overcome warfarin resistance in rats. Treatment of 'superwarfarin' ingestion includes monitoring of INR and treatment with phytomenadione as the coagulopathy may persist for months. Common causes of 'superwarfarin' poisoning include accidental ingestion (usually in children), attempted suicide and deliberate self-poisoning with denial (Munchausen syndrome).