Naproxen

Naproxen is a propionic-acid nonsteroidal anti-inflammatory drug with historical veterinary use in musculoskeletal disease. Its main veterinary applications have involved horses, particularly soft-tissue inflammation and associated lameness. Species differences in elimination are substantial, with prolonged persistence in dogs. Its role in current veterinary treatment is comparatively limited.

Group

Nonsteroidal anti-inflammatory drug

Mechanism of Action

Naproxen inhibits cyclooxygenase enzymes and reduces synthesis of prostaglandins involved in inflammatory signaling and sensitization of pain receptors. This provides analgesic, anti-inflammatory and antipyretic activity. In musculoskeletal disease, reduced mediator activity can lessen pain and swelling. The duration of exposure varies markedly with species-specific metabolism and elimination.

Dose Rates

Horses

Use / stage	Dose	Route	Schedule	Instructions
Musculoskeletal pain	10 mg/kg	PO	Every 12 h	Up to 14 days; Historical veterinary regimen; use requires gastrointestinal and renal risk assessment.
Alternative musculoskeletal pain regimen	10 mg/kg	PO	Every 24 h
Historical parenteral loading before oral therapy — Loading	5 mg/kg	IV	Once	Slow IV using the former equine injection; follow the separately prescribed oral course. The old injectable product is no longer described as marketed.

Dogs

Use / stage	Dose	Route	Schedule	Instructions
Historical musculoskeletal pain regimen	Reference only	PO		Historical regimen: 5 mg/kg initially, then 2 mg/kg every 48 hours. Published guidance states use is not recommended in dogs because prolonged elimination increases serious toxicity risk.

Rabbits

Use / stage	Dose	Route	Schedule	Instructions
Septic arthritis pain or inflammation	Reference only	PO		Up to 21 days; 2.4 mg/mL in drinking water for 21 days was described. Water intake and systemic exposure vary; this is a drinking-water concentration, not a body-weight prescription.

Indications

Treatment of selected equine myositis or other inflammatory soft-tissue musculoskeletal disease with associated pain and lameness.
Historical treatment of selected equine osteoarthritis-associated pain and inflammation, with limited modern comparative clinical evidence.

Contraindications

Patients with gastrointestinal ulceration or bleeding
Dehydration or significant renal compromise

Interactions

Do not combine with other NSAIDs or corticosteroids.
May interfere with diuretics and ACE inhibitors.
Probenecid can increase naproxen exposure and half-life.
Anticoagulants increase bleeding risk; aminoglycosides increase renal risk.
Methotrexate toxicity may be increased; bisphosphonates add GI injury risk.

Adverse effects

Gastrointestinal ulceration or hemorrhage
Renal injury

Toxicity

Dogs eliminate naproxen slowly and can develop severe toxicity after human OTC exposure. Treat overdose as a prolonged gastrointestinal and renal risk.

Preparations

Preparation	Form	Strength	Route
Naproxen tablets 250 mg	Tablet	250 mg / tablet	PO
Naproxen tablets 375 mg	Tablet	375 mg / tablet	PO
Naproxen tablets 500 mg	Tablet	500 mg / tablet	PO
Naproxen oral suspension 25 mg/mL	Oral Liquid	25 mg / mL	PO

Monitoring and Administration

Assess hydration, renal function and gastrointestinal signs. Monitor for vomiting, melena and appetite loss.

Do not equate naproxen sodium tablet mass with naproxen mass: 220 mg naproxen sodium corresponds to 200 mg naproxen. Human tablet doses must not be extrapolated to dogs.

Canine exposures above 5 mg/kg can cause GI signs or ulcers; significant renal injury has occurred from about 10–25 mg/kg and neurologic signs above 50 mg/kg. These are toxicity observations, not safe boundaries.

Significant overdose requires gastrointestinal and renal assessment, tailored decontamination when appropriate, gastroprotection and fluid/electrolyte management. Continued GI monitoring/support may be needed for 10–14 days.