5-Fluorouracil (5-FU) is used in human medicine for the mangement of dermal neoplasms and actinic keratoses. It is typically available in a 5% cream and only a small dose causes severe poisoning in cats and dogs. 5-FU poisoning is characterised by gastrointestinal signs, neurotoxicity and bone marrow depression. A recent letter in the Journal of the American Veterinary Medical Association (Glass EN, Song RB, Kent M. JAVMA. 2019 254(7):787-788) highlights the risk of 5-FU poisoning in pets and the lack of knowledge of owners and physicians of the dangers. The authors also call on the American Veterinary Medical Association to lobby for product labelling that clearly details the hazards of 5-FU ingestion by dogs.

We are very familar with 5-FU poisoning in dogs and last year  presented our cases at the European Association of Poisons Centres and Clinical Toxicologists (EAPCCT) Congress.

We had 33 cases with follow up and only four dogs remained asymptomatic. Symptomatic dogs developed neurological, gastrointestinal, cardiovascular or respiratory complications. Active bleeding and coagulopathies were also frequently reported. The most predominant sign was vomiting (57%, n=19); convulsions occurred in 17 dogs (51.5%).

Overall, 7 dogs died (21%), 14 were euthanized (42%), and 8 made a full recovery (24%). The dose ingested in surviving dogs was only estimated in one case and was 0.8 mg/kg. The overall fatality rate in symptomatic cases was high (72.4%), and the most common signs reported in these dogs were vomiting (87.5%), convulsions (50%), and bleeding complications (37.5%). Time to death was reported in 3 cases and was 11.5, 16.5 and 72 hours. The dose was estimated in three dogs that died and was 2.5, 3.3-6.7 and 4.8-9.5 mg/kg. (These doses are equivalent to only 0.05 to 0.2 g of cream per kg). Time to euthanasia was reported in 7 cases with a mean of 15 hours and range of 4 to 32 hours; euthanasia was typically due to progression of signs and poor prognosis. The dose ingested was estimated in 6 dogs that were euthanized with a mean of 5.4 mg/kg and a range of 2.2-8.3 mg/kg.

The EAPCCT abstracts, which include other veterinary subjects,  are available online.