Is Naproxen safe for dogs and cats?

Naproxen is one of the most dangerous OTC NSAIDs for dogs, with a narrow therapeutic index and a prolonged plasma half-life (74 hours in dogs vs. 14 hours in humans) due to extensive enterohepatic recirculation. The recommended veterinary dose is 2–5 mg/kg, but even small doses of human OTC naproxen (220 mg Aleve tablets) can cause serious toxicity in small-to-medium dogs. A single 220 mg tablet represents approximately 10–22 mg/kg in a 10–20 kg dog — already within the toxic range. Toxic effects in dogs are dominated by GI pathology: acute gastric and intestinal ulceration, melena, hematemesis, and GI perforation. Renal papillary necrosis is a serious concern at higher doses (COX-mediated loss of prostaglandin-dependent renal autoregulation). Hepatotoxicity, CNS effects (ataxia, seizures), and electrolyte imbalances may occur in severe overdose. Naproxen is a frequent cause of NSAID toxicosis in dogs because Aleve and combination cold medications containing naproxen are common in households. ASPCA APCC reports naproxen as a top-10 pharmaceutical toxin for dogs.

Naproxen is extremely toxic to cats. Cats are highly sensitive to NSAID toxicity due to limited glucuronidation capacity and reduced ability to clear naproxen and its metabolites. The enterohepatic recirculation that prolongs naproxen's half-life in dogs is even more pronounced in cats; plasma half-life in cats can exceed 100 hours. Any human dose of naproxen is potentially lethal to cats — even small fragments of an Aleve tablet. Clinical signs in cats include progressive gastric ulceration (sometimes with perforation), severe acute renal failure, CNS depression, and anemia from GI blood loss. Acute renal failure following naproxen ingestion in cats can be irreversible. Given the extreme sensitivity, veterinary professionals consider naproxen absolutely contraindicated in cats under any circumstances. Emergency management includes decontamination (if early), aggressive IV fluid support to maintain renal perfusion, GI protectants (sucralfate, omeprazole), and monitoring for renal and hematologic deterioration.