A 59-year-old patient attended our outpatient department in extreme distress, and reported how his pet dog had become unwell and had been euthanized following accidental ingestion of 5-fluorouracil (5-FU). The patient, who was on long-term azathioprine for Crohn disease, was using Efudix â cream to treat several keratotic lesions on his forehead, and had applied the cream and gone to bed. He was awoken soon after by his pet dog licking his forehead (and therefore the cream). The dog was a Jack Russell terrier type weighing approximately 7 kg, and very soon after ingestion of the cream, he exhibited signs of ataxia, tremors and vomiting. Topical 5-FU ointment is frequently prescribed by general practitioners and in plastic surgery and dermatology outpatient clinics to treat keratotic lesions and both premalignant and malignant skin cancers. 1 Topical application results in minimal systemic absorption, although systemic toxicity has been reported in patients with dihydropyrimidine dehydrogenase deficiency. 2 5-FU cream is commonly available in the UK as Efudix â (5% w/w 5-FU; 50 mg/mL or 2 g in a 40 g tube; Meda Pharmaceuticals Ltd., Bishop’s Stortford, Hertfordshire, UK) or Actikerall â (5-FU plus 10% salicylic acid; Almirall Ltd, Uxbridge, Middlesex, UK).

In our practice, patients are given verbal advice explaining what to expect, the application, regimen, sideeffects and precautions, reinforced with an advice leaflet. They also have access to the patient advice leaflet that is supplied with the 5-FU ointment. Both verbal and written types of advice stress the importance of washing the hands after applying the cream to prevent accidental oral ingestion. However, it has not been our practice to date to warn patients about 5-FU toxicity to pets. 5-FU is toxic to animals in very small amounts, with toxic doses reported at 5mg/kg, a minimum lethal threshold of 20 mg/kg and doses of≥ 40 mg/kg reported to be uniformly fatal. 3 The veterinary literature has