Naproxen, most commonly known by the names Midol® and Aleve®, is a nonsteroidal anti-inflammatory drug (NSAID). It works by reducing hormones that cause inflammation and pain. Like other NSAIDs, it can be used therapeutically in dogs but overdoses and toxicities are common.
Naproxen has a narrow margin of safety. Unlike humans and many other species who eliminate naproxen in urine, dogs require extensive enterohepatic recirculation and eliminate naproxen in the feces. This accounts for a long half-life and increased risk of toxicity.
Toxicity can result in gastrointestinal ulcers and/or acute kidney failure. We have historically considered the toxic dose of Naproxen to be greater than 25 mg/kg.
We have historically considered the toxic dose of Naproxen to be greater than 25 mg/kg but in recent consultations with Pet Poison centers, have learned doses greater than 10 mg/kg are considered toxic and have been associated with the development of clinical signs.