Naproxen
Also known as: Aleve · Anaprox · EC-Naprosyn · Midol Extended Relief · Naprelan · Equiproxen · naproxeneum · RS-3540 · RS-3650 · naproxen sodium
Reviewed by the VetSheet Veterinary TeamUpdated Apr 5, 2026Evidence-based veterinary reference
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Dosing by species
🌎 NA — North America🌍 EU — Europe
Dogs
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Osteoarthritis and musculoskeletal inflammatory diseases (Last resort) | 2 mg/kg PO every other day (q48h) | PO | q48h | — | 🌎 NA |
- Osteoarthritis and musculoskeletal inflammatory diseases (Last resort): Because of the difficulty in accurately dosing naproxen and its potential for adverse effects, use only when FDA-approved and safer NSAIDs have been ineffective.
Small Mammals
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Septic arthritis pain; inflammation (Rabbits) | 2.4 mg/mL in drinking water for 21 days | PO | Continuous | 21 days | 🌎 NA |
- Septic arthritis pain; inflammation (Rabbits): Dose specific to rabbits.
Horses
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Myositis and soft tissue diseases of the musculoskeletal system | 5 mg/kg by slow IV, then 10 mg/kg, PO (top dressed in feed) twice daily for up to 14 days or 10 mg/kg, PO (top dressed in feed) twice daily for up to 14 consecutive days. | IV, PO | q12h | Up to 14 days | 🌎 NA |
| Systemic therapies for joint disease | 10 mg/kg PO daily | PO | q24h | — | 🌎 NA |
- Myositis and soft tissue diseases of the musculoskeletal system: ARCI UCGFS Class 4 Drug. Veterinary product no longer commercially available.
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Overview
Naproxen is a nonsteroidal anti-inflammatory drug (NSAID) belonging to the propionic acid class, structurally similar to ibuprofen and ketoprofen.
- Veterinary Use: Its use in veterinary medicine has been largely superseded by newer, safer, and more COX-2 selective NSAIDs.
- Toxicity Risk: It is notoriously toxic to dogs due to its exceptionally long half-life (74 hours) and extensive enterohepatic recirculation, leading to a very narrow therapeutic index. Many clinicians strongly advise against its use in dogs.
- Equine Use: Previously used for musculoskeletal pain, myositis, and soft tissue diseases in horses, but the veterinary-specific product (Equiproxen®) is no longer marketed in the USA.
Mechanism of action
Naproxen exerts its analgesic, anti-inflammatory, and antipyretic effects by inhibiting the cyclooxygenase (COX) enzymes.
- Arachidonic Acid → COX-1 and COX-2 inhibition → Decreased synthesis of prostaglandins and thromboxanes.
- The reduction in pro-inflammatory prostaglandins mitigates inflammation, pain, and fever.
- Because naproxen is a non-selective COX inhibitor, it also blocks the constitutive, protective prostaglandins (via COX-1) in the gastric mucosa and kidneys. This mechanism explains its high propensity for causing gastrointestinal ulceration and renal toxicity, particularly in sensitive species like dogs and cats.
Safety & warnings
Contraindications
- Active GI ulcers
- History of hypersensitivity to naproxen or other NSAIDs
- Pre-existing hematologic, renal, or hepatic disease
Adverse effects
- GI distress (anorexia, vomiting, diarrhea)
- Gastrointestinal ulcers and perforation
- Melena and bloody vomitus
- Renal effects (nephritis, nephrotic syndrome, fluid retention)
- Hepatic effects (increased liver enzymes)
- Hematologic effects (hypoproteinemia, decreased hematocrit, anemia)
- CNS effects (neuropathies, lethargy, depression)
Precautions
WARNING: Extremely narrow therapeutic index in dogs. Use is generally discouraged unless all FDA-approved, safer NSAIDs have failed.
- Relatively Contraindicated: Patients with a history of or pre-existing hematologic, renal, or hepatic disease.
- Caution: Use cautiously in patients with a history of GI ulcers or heart failure (may cause fluid retention).
- Infection: Animals suffering from inflammation secondary to concomitant infection should receive appropriate antimicrobial therapy alongside NSAID treatment.
Drug interactions
Increased risk for nephrotoxicity
Increased risk for bleeding
Decreased plasma levels of naproxen and increased likelihood of GI adverse effects (blood loss). Concomitant use is not recommended.
May increase risk for GI ulceration
Concomitant administration significantly increases the risks for GI adverse effects and ulceration
Naproxen may reduce the saluretic and diuretic effects of furosemide
Potential displacement leading to increased serum levels and duration of action of the displaced drug
Serious toxicity has occurred; use together with extreme caution
May cause a significant increase in serum levels and half-life of naproxen
Monitoring
- Analgesic/anti-inflammatory efficacy
- GI signs: appetite, feces (occult blood, diarrhea)
- PCV (packed cell volume) and hematocrit if indicated or on chronic therapy
- WBCs if indicated or on chronic therapy
- Renal and hepatic function panels (especially in dogs)
Pharmacokinetics
Half-life
Absorption
Horses: 50% bioavailability after oral dosing; absorption is not altered by food. Dogs: Rapid oral absorption with 68-100% bioavailability.
Distribution
Highly bound to plasma proteins (99% in humans). Crosses the placenta and enters milk at about 1% of serum levels.
Metabolism
Metabolized in the liver.
Elimination
Detectable in the urine for at least 48 hours in the horse after an oral dose.
Overdose
Toxicity is a major concern, particularly in dogs and cats.
- Dogs: The reported oral LD50 is >1000 mg/kg, but clinical toxicity occurs at much lower doses.
- >5 mg/kg: Gastrointestinal signs and GI ulceration.
- >25 mg/kg (some dogs as low as 10 mg/kg): Significant renal damage.
- >50 mg/kg: Neurologic signs.
- Clinical Signs: Vomiting (often bloody), lethargy, anorexia, diarrhea, melena, anemia, and elevated renal/hepatic values.
- Treatment:
- Decontamination: Emesis and/or activated charcoal if recent ingestion.
- GI Protection: Misoprostol and sucralfate are recommended for 10-14 days post-exposure.
- Renal Protection: Fluid diuresis should be considered if renal effects are expected.
- Supportive Care: Monitor electrolyte and fluid balance carefully; manage renal failure using established guidelines.
Available products
Formulations
- Oral tablets
- Gelcaps
- Capsules
- Delayed/controlled-release tablets
- Oral suspension
- Injection (historically available for horses)
Veterinary
- None currently marketed in the USA (Equiproxen® is discontinued)
Human-labeled
- Naproxen Oral Tablets/Gelcaps/Capsules: 200 mg, 250 mg, 375 mg, 500 mg
- Naproxen Delayed/Controlled-release Tablets: 375 mg, 500 mg, 750 mg
- Naproxen Oral Suspension: 125 mg/5 mL
Regulatory status
No regulatory data for: 🇺🇸 US · 🇪🇺 EU · 🇬🇧 UK · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Storage & stability
Store in well-closed, light-resistant containers at room temperature. Avoid temperatures above 40°C (104°F).
Client information
DANGER: Never give human over-the-counter pain relievers like Aleve® to your pets without explicit veterinary instructions. Naproxen is highly toxic to dogs and cats.
- If your pet is prescribed naproxen, strictly adhere to the dosing schedule (which may be as infrequent as every other day for dogs).
- Stop the medication and contact your veterinarian immediately if you notice:
- Loss of appetite or lethargy/depression
- Vomiting (especially if it contains blood or looks like coffee grounds)
- Diarrhea or black, tarry stools
- Changes in drinking or urination habits
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturer’s current label.