Is Carprofen safe for dogs and cats?

Carprofen (Rimadyl, Novox) is one of the most widely prescribed veterinary NSAIDs in dogs, FDA-approved for the relief of pain and inflammation associated with osteoarthritis and for the control of postoperative pain. Carprofen has a favorable safety profile in most dogs at therapeutic doses (2.2 mg/kg twice daily or 4.4 mg/kg once daily). The principal clinical concern is idiosyncratic hepatotoxicity — a rare but serious hepatocellular necrosis that was identified in the post-approval surveillance period, occurring at a higher-than-expected frequency in Labrador Retrievers (though not exclusively). FDA issued a safety advisory and added enhanced labeling with recommendations for baseline and periodic liver enzyme monitoring in dogs receiving long-term carprofen. The hepatotoxicity is not dose-dependent and may represent a metabolic idiosyncrasy. GI ulceration, renal toxicity, and hematological effects are class-related NSAID risks; concurrent corticosteroid use is contraindicated. Carprofen was formerly a human NSAID withdrawn from the human market in Europe in the 1980s but continues in wide veterinary use.

Carprofen is not FDA-approved for use in cats in the US. Cats have reduced hepatic glucuronidation capacity relative to dogs, leading to prolonged drug half-life and accumulation of carprofen and its metabolites; this pharmacokinetic difference predisposes cats to NSAID toxicity including GI hemorrhage, renal failure, and hepatotoxicity at doses well-tolerated in dogs. Extra-label feline use of carprofen carries significant risk and requires very cautious dosing, monitoring, and limiting to short courses. ASPCA Animal Poison Control Center lists carprofen among NSAIDs causing serious toxicosis in cats at dog-appropriate doses. The EU has approved carprofen as a single perioperative injection in cats (not repeated dosing). The primary risk scenario in households is cats accessing dog carprofen tablets, which can cause acute toxicosis.