Warfarin

Generic Name: Warfarin
Brand Name: Coumadin

Warfarin is an anticoagulant used in both human and veterinary medicine. In dogs, it is used primarily for long-term thromboprophylaxis. Current evidence is controversial, but not recommended.

Despite it’s use in veterinary medicine, acute overdosages of warfarin may result in life-threatening hemorrhage.

It’s important to note that a lag time occurs after warfarin is ingested. It could, therefore, take 2-5 days before signs of toxicity occur.

Signs and symptoms of toxicity: extreme fatigue, refusal to eat, bloody urine, and vomiting. Due to the nature of warfarin’s mechanism of action, it may take 2-5 days before signs of toxicity occur. Animals should be monitored accordingly.

Toxic consumption: In both dogs and cats, doses of 5-50 mg/kg have been associated with toxicity. Cumulative toxic doses of warfarin have been reported as 1-5 mg/kg for 5 to 15 days in dogs and 1 mg/kg for 7 days in cats.

Dogs: Warfarin Toxic Consumption
X-Small Yorkie, Chihuahua	Small Pug, Boston Terrier, Poodle	Medium Beagle, Scottish Terrier	Large Boxer, Cocker Spaniel	X-Large Labrador & Golden Retrievers, German Shepherd	XX-Large Great Dane, St. Bernard
1 – 10 lbs. (0.45 – 4.6 kg)	11 – 25 lbs. (5 – 11.4 kg)	26 – 40 lbs. (11.8 – 18.2 kg)	41 – 70 lbs. (18.6 – 31.8 kg)	71 – 90 lbs. (32.3 – 40.9 kg)	91 – 110 lbs. (41.4 – 50 kg)
> 2.25 mg	> 25 mg	> 59 mg	> 93 mg	> 161.5 mg	> 207 mg

Cats: Warfarin Toxic Consumption
Most Cats	Large Cats
1 – 10 lbs. (0.45 – 4.6 kg)	11 – 25 lbs. (5 – 11.4 kg)
> 2.25 mg	> 25 mg

References:
– Papich MG. Saunders Handbook of Veterinary Drugs: Small and Large Animal. 3rd ed. St. Louis, MS: Elsevier Saunders; 2011.
– Warfarin Sodium. In: Plumb’s Veterinary Drugs. Tulsa (OK): Educational Concepts, L.L.C. [updated 8/14; accessed 8/27/15]. https://www.plumbsveterinarydrugs.com/#!/monograph/1721