Rimadyl (Carprofen)

Non-Steroidal Anti-Inflammatory Drug (NSAID) Propionic acid derivative

Dosage & Administration Guidelines

Species Route Dose Frequency Duration & Clinical Notes
Dog PO 2.2 mg/kg (1 mg/lb) q12h Duration: For osteoarthritis: 7-14 days initially, then as needed. For postoperative pain: 3-7 days.
Notes: Administer with food to reduce GI upset. Use the lowest effective dose for the shortest duration.
Dog IV 4.4 mg/kg (2 mg/lb) Once Duration: Preoperative or intraoperative for postoperative pain management.
Notes: Administer slowly over 1-2 minutes. May be repeated after 24 hours if needed.
Cat PO 4 mg/kg q24h Duration: Short-term (1-3 days) for pain management.
Notes: Not approved; use with caution due to prolonged half-life. Monitor for adverse effects.
Horse IV 0.7 mg/kg q24h Duration: Up to 5 days for musculoskeletal pain.
Notes: Administer slowly. Not for long-term use.
Horse PO 2 mg/kg q24h Duration: Up to 5 days.
Notes: Oral bioavailability is lower; adjust dose accordingly.
Cattle IV 1.4 mg/kg Once Duration: Single dose for pain and inflammation.
Notes: Not approved; extra-label use requires veterinary oversight and extended withdrawal times.

Clinical Indications & Species Uses

General Indications
  • Pain and inflammation associated with musculoskeletal disorders
  • Postoperative pain management
Dog (Canine)
  • Relief of pain and inflammation associated with osteoarthritis
  • Postoperative pain management (e.g., orthopedic and soft tissue surgery)
Horse (Equine)
  • Relief of pain and inflammation associated with musculoskeletal disorders (e.g., colic, laminitis, post-surgical pain)

Pharmacology & Mechanism of Action

Drug Class: Non-Steroidal Anti-Inflammatory Drug (NSAID) | Pharmacological Group: Propionic acid derivative

Mechanism of Action: Carprofen is a non-selective cyclooxygenase (COX) inhibitor with preferential selectivity for COX-2 over COX-1. It inhibits the synthesis of prostaglandins, which are mediators of inflammation, pain, and fever. By reducing prostaglandin production, carprofen decreases inflammation and pain associated with musculoskeletal disorders and postoperative pain. It also has some analgesic and antipyretic effects.

Pharmacodynamics: Carprofen exhibits anti-inflammatory, analgesic, and antipyretic activity. It is more selective for COX-2 than COX-1, which may reduce the risk of gastrointestinal ulceration compared to non-selective NSAIDs. However, it still carries risks of renal and hepatic adverse effects. The onset of action is typically within 1-2 hours after oral administration, with peak effects at 2-4 hours. The duration of action is approximately 12-24 hours in dogs.

⚡ Pharmacokinetics Summary

Absorption: Carprofen is well absorbed after oral administration in dogs, with a bioavailability of approximately 90%. Peak plasma concentrations occur within 1-3 hours. In horses, oral absorption is slower and less complete. In cattle, oral bioavailability is lower and variable.
Distribution: Carprofen is highly protein-bound (>99%) in plasma. It distributes widely into tissues, with higher concentrations in inflamed tissues. It crosses the blood-brain barrier to a limited extent. Volume of distribution is approximately 0.1-0.2 L/kg in dogs.
Metabolism: Carprofen is extensively metabolized in the liver, primarily via oxidation and conjugation. The major metabolic pathways involve hydroxylation and glucuronidation. In dogs, the main metabolite is the S-enantiomer, which is pharmacologically active. In cats, metabolism is slower, leading to a longer half-life.
Excretion: Carprofen is excreted primarily in the feces (approximately 70-80%) and to a lesser extent in the urine. In dogs, the elimination half-life is approximately 8 hours (range 4-12 hours). In cats, the half-life is significantly longer, around 20-30 hours. In horses, the half-life is approximately 30 hours.
Half-Life: Dog: 8 hours (range 4-12); Cat: 20-30 hours; Horse: 30 hours; Cattle: 1-2 hours (short)
Bioavailability: Oral: ~90% in dogs; ~50-70% in horses; variable in cattle
Protein Binding: >99% in dogs and cats

Available Formulations & Strengths

Oral Tablet 25 mg, 75 mg, 100 mg (PO)
Chewable Tablet 25 mg, 75 mg, 100 mg (PO)
Injectable Solution 50 mg/mL (IV)

Contraindications & Clinical Warnings

Contraindications:
  • Known hypersensitivity to carprofen or other NSAIDs
  • Active gastrointestinal ulceration or bleeding
  • Renal or hepatic impairment
  • Dehydration or hypovolemia
  • Concurrent use of corticosteroids or other NSAIDs
  • Bleeding disorders (e.g., coagulopathies)
  • Pregnancy or lactation (unless specifically indicated)
Warnings & Clinical Precautions:
  • Use with caution in animals with pre-existing renal, hepatic, or cardiac disease.
  • Monitor for signs of gastrointestinal toxicity (vomiting, diarrhea, melena).
  • Use the lowest effective dose for the shortest duration.
  • In cats, use with extreme caution due to prolonged half-life; monitor closely.
  • In horses, do not use in cases of colic due to risk of renal damage.
  • Avoid use in animals with hypotension or shock.
  • Do not administer with other NSAIDs or corticosteroids.
  • In food animals, observe withdrawal times and follow extra-label regulations.

Adverse Effects & Reactions

Common:

  • Vomiting
  • Diarrhea
  • Loss of appetite
  • Lethargy
  • Increased thirst

Serious / Severe:

  • Gastrointestinal ulceration or perforation
  • Renal failure
  • Hepatotoxicity
  • Bleeding disorders
  • Anaphylaxis

Rare:

  • Blood dyscrasias
  • Neurological signs (ataxia, seizures)
  • Dermatological reactions (erythema, pruritus)

Key Drug Interactions

Interacting Drug / Class Clinical Effect & Mechanism Severity
Corticosteroids (e.g., prednisone, dexamethasone) Increased risk of gastrointestinal ulceration and renal toxicity. High
Other NSAIDs (e.g., aspirin, meloxicam) Additive risk of gastrointestinal and renal toxicity. High
Anticoagulants (e.g., warfarin, heparin) Increased risk of bleeding. High
ACE inhibitors (e.g., enalapril) Reduced renal function and increased risk of renal toxicity. Moderate
Diuretics (e.g., furosemide) Reduced renal perfusion and increased risk of renal toxicity. Moderate
Aminoglycoside antibiotics (e.g., gentamicin) Increased risk of nephrotoxicity. Moderate

Overdose & Toxicity Management

Signs of Toxicity:

  • Vomiting
  • Diarrhea (possibly bloody)
  • Lethargy
  • Loss of appetite
  • Abdominal pain
  • Seizures
  • Coma
  • Renal failure
  • Liver failure

Emergency Treatment Protocol: Induce emesis if within 2 hours of ingestion and the animal is conscious. Administer activated charcoal to reduce absorption. Provide symptomatic and supportive care: intravenous fluids to maintain renal perfusion, gastroprotective agents (e.g., sucralfate, H2 antagonists, proton pump inhibitors), and monitoring of renal and hepatic function. In severe cases, consider hemodialysis or peritoneal dialysis.

Food Animal Withdrawal Times

🥩 Meat: 21 days🥛 Milk: 7 days

Withdrawal times are not established for carprofen in food animals in many countries. Extra-label use requires extended withdrawal periods. Consult regulatory guidelines. For cattle, a meat withdrawal of 21 days and milk withdrawal of 7 days are commonly recommended, but these may vary by jurisdiction.

Storage, Handling & Regulatory Information

Storage Temperature: Store at controlled room temperature 20-25°C (68-77°F), excursions permitted between 15-30°C (59-86°F).

Handling & Special Conditions: Protect from moisture. Keep in a tightly closed container.

Dispensing Status: Prescription Required (Rx Only)

Approval Status: Approved for use in dogs (Rimadyl) by the FDA. Not approved for cats, horses, cattle, or other species.

Extra-Label (Off-Label) Use: In the US, carprofen is approved for dogs only. Extra-label use in other species is permitted under AMDUCA (Animal Medicinal Drug Use Clarification Act) with a valid veterinarian-client-patient relationship. For food animals, extended withdrawal times must be observed.

Clinical Pearls & Practice Notes

💡 Clinical Insights: Carprofen is a widely used NSAID in veterinary medicine, primarily for dogs. It is effective for managing pain and inflammation associated with osteoarthritis and postoperative pain. It is generally well-tolerated, but adverse effects, particularly gastrointestinal and renal, can occur. Use the lowest effective dose for the shortest duration. In cats, carprofen has a prolonged half-life and is not approved; use only if no alternatives are available and with close monitoring. In horses, it is used off-label for musculoskeletal pain, but caution is advised. For food animals, extra-label use requires careful consideration of withdrawal times. Always monitor for signs of toxicity and educate owners on the risks.

References & Literature

  • 📚 Plumb's Veterinary Drug Handbook
  • 📚 Papich Veterinary Pharmacology and Therapeutics
  • 📚 Compendium of Veterinary Products (CVP)