Flunixin Meglumine

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

Dosage & Administration Guidelines

Species Route Dose Frequency Duration & Clinical Notes
Dog IV, IM, SC, PO 1 mg/kg (0.5-1 mg/kg) Once daily (q24h) Duration: Up to 3 days (max 3 days)
Notes: IV route preferred for rapid effect. Not approved for oral use in dogs; use with caution. Do not exceed 3 days.
Cat IV, IM, SC 1 mg/kg (0.5-1 mg/kg) Once daily (q24h) Duration: Up to 3 days (max 3 days)
Notes: Off-label use; use with caution due to increased risk of renal and GI adverse effects. Not approved for cats.
Horse IV 1.1 mg/kg (1.0-1.1 mg/kg) Once daily (q24h) Duration: Up to 5 days (for musculoskeletal pain); for colic, may repeat once if needed
Notes: IV administration only. For colic, administer slowly. Do not exceed 5 days. Use with caution in dehydrated or hypovolemic horses.
Cattle IV 2.2 mg/kg (1.1-2.2 mg/kg) Once daily (q24h) Duration: Up to 3 days
Notes: IV administration only. For respiratory disease, use as adjunct to antimicrobial therapy. Do not exceed 3 days.
Small Ruminants (Sheep, Goats) IV, IM 2.2 mg/kg Once daily (q24h) Duration: Up to 3 days
Notes: Off-label use; use with caution. Not approved for these species.
Swine IM 2.2 mg/kg Once daily (q24h) Duration: Up to 3 days
Notes: Off-label use; not approved in swine in the US. Use with caution.

Clinical Indications & Species Uses

General Indications
  • Non-steroidal anti-inflammatory drug for relief of pain, inflammation, and fever in various species
Dog (Canine)
  • Management of pain and inflammation associated with musculoskeletal disorders
  • Post-operative pain relief
  • Pyrexia of various origins
Cat (Feline)
  • Management of pain and inflammation (off-label; not FDA-approved for cats)
  • Post-operative pain relief (off-label)
Horse (Equine)
  • Alleviation of pain and inflammation associated with musculoskeletal disorders
  • Relief of visceral pain associated with colic
  • Treatment of endotoxemia and septic shock
  • Reduction of fever
Cattle (Bovine)
  • Control of acute inflammation associated with respiratory disease
  • Reduction of fever in bovine respiratory disease complex
  • Adjunct therapy in acute mastitis
  • Management of pain associated with lameness and other musculoskeletal conditions
Small Ruminants (Sheep / Goat)
  • Management of pain and inflammation (off-label)
  • Reduction of fever in respiratory disease (off-label)

Pharmacology & Mechanism of Action

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

Mechanism of Action: Flunixin meglumine is a potent, non-narcotic analgesic with anti-inflammatory, antipyretic, and anti-endotoxic properties. It acts primarily by reversible inhibition of cyclooxygenase (COX) enzymes, both COX-1 and COX-2, thereby blocking the conversion of arachidonic acid into prostaglandins and thromboxanes. This reduces the production of pro-inflammatory mediators, decreases pain sensation, and lowers fever. Additionally, flunixin has been shown to inhibit the effects of endotoxins by reducing the release of inflammatory cytokines and eicosanoids, which is particularly beneficial in endotoxemia and septic shock.

Pharmacodynamics: Flunixin produces potent analgesic and anti-inflammatory effects that are more pronounced than many other NSAIDs. It has a rapid onset of action, with analgesia occurring within 15 minutes after intravenous administration in horses. Its anti-endotoxic effects are notable: it prevents endotoxin-induced hemodynamic changes, reduces the production of thromboxane B2 and prostacyclin, and improves survival in experimental models of endotoxemia. The duration of action is typically 24-36 hours, depending on the species and dose. Flunixin also has a significant antipyretic effect by acting on the hypothalamic heat-regulating center.

⚡ Pharmacokinetics Summary

Absorption: Flunixin is well absorbed after oral, intramuscular, and subcutaneous administration. In horses, oral bioavailability is approximately 80%, while in cattle it is around 60-80%. Peak plasma concentrations are reached within 1-2 hours after oral dosing and 30 minutes after intramuscular injection. In dogs and cats, oral absorption is rapid, with peak levels in 1-2 hours.
Distribution: Flunixin is highly bound to plasma proteins (approximately 90%). It distributes widely into tissues, with high concentrations in the liver, kidneys, and inflammatory exudates. It crosses the blood-brain barrier to a limited extent. In lactating animals, it is excreted into milk in small amounts.
Metabolism: Flunixin undergoes hepatic metabolism, primarily via hydroxylation and conjugation. The major metabolite is 5-hydroxy-flunixin, which is pharmacologically inactive. Metabolism is species-dependent, with dogs and cats metabolizing it more rapidly than horses and cattle.
Excretion: Excretion is primarily renal, with both unchanged drug and metabolites eliminated in the urine. A small portion is excreted in feces. In cattle, the elimination half-life is approximately 3-8 hours, while in horses it is about 1.6-2.5 hours. In dogs, the half-life is around 3.7 hours, and in cats it is approximately 2.5 hours.
Half-Life: Horse: 1.6-2.5 hours; Cattle: 3-8 hours; Dog: 3.7 hours; Cat: 2.5 hours; Swine: 4-6 hours
Bioavailability: Oral: 80% in horses, 60-80% in cattle; IM/SC: nearly 100%
Protein Binding: Approximately 90% bound to plasma proteins

Available Formulations & Strengths

Injectable Solution 50 mg/mL (as flunixin meglumine) (IV, IM, SC)
Oral Paste 1500 mg/30g syringe (for horses) (PO)
Oral Granules 250 mg/g (for horses) (PO)
Oral Tablet Not commonly available; some compounded forms may exist (PO)

Contraindications & Clinical Warnings

Contraindications:
  • Known hypersensitivity to flunixin meglumine or other NSAIDs
  • Active gastrointestinal ulceration or bleeding
  • Renal impairment or renal disease
  • Hepatic impairment
  • Hypotension, hypovolemia, or dehydration
  • Bleeding disorders (e.g., coagulopathies)
  • Concurrent use of other NSAIDs or corticosteroids
  • Pregnancy (especially late gestation) unless benefits outweigh risks
  • Use in neonates or young animals (age-related risk of renal and GI toxicity)
Warnings & Clinical Precautions:
  • Do not exceed recommended dose or duration; prolonged use increases risk of adverse effects.
  • Use with caution in animals with pre-existing renal, hepatic, or cardiac disease.
  • Monitor for signs of gastrointestinal ulceration, renal toxicity, or bleeding.
  • In horses, do not use in cases of colic associated with shock or dehydration; ensure adequate hydration.
  • In cattle, do not administer intramuscularly or subcutaneously; IV only.
  • Avoid use in animals with suspected or confirmed gastric ulceration.
  • Use with caution in geriatric animals.
  • May mask signs of infection or fever; monitor appropriately.
  • In food animals, observe withdrawal times.
  • Do not use in animals with known hypersensitivity to NSAIDs.

Adverse Effects & Reactions

Common:

  • Gastrointestinal upset (vomiting, diarrhea, anorexia)
  • Decreased appetite
  • Lethargy
  • Injection site reactions (pain, swelling)

Serious / Severe:

  • Gastrointestinal ulceration and perforation
  • Renal papillary necrosis and acute renal failure
  • Hepatotoxicity
  • Bleeding disorders (prolonged bleeding time)
  • Bone marrow suppression (rare)
  • Anaphylaxis (rare)

Rare:

  • Blood dyscrasias (thrombocytopenia, leukopenia)
  • Neurological signs (ataxia, seizures)
  • Dermatological reactions (rash, pruritus)

Key Drug Interactions

Interacting Drug / Class Clinical Effect & Mechanism Severity
Other NSAIDs (e.g., aspirin, carprofen, meloxicam) Additive risk of gastrointestinal ulceration, renal toxicity, and bleeding. High
Corticosteroids (e.g., dexamethasone, prednisone) Increased risk of gastrointestinal ulceration and renal toxicity. High
Anticoagulants (e.g., heparin, warfarin) Increased risk of bleeding due to inhibition of platelet function. High
Aminoglycoside antibiotics (e.g., gentamicin) Increased risk of nephrotoxicity. Moderate
Diuretics (e.g., furosemide) Reduced diuretic efficacy and increased risk of renal toxicity due to decreased renal blood flow. Moderate
ACE inhibitors (e.g., enalapril) Reduced antihypertensive effect and increased risk of renal impairment. Moderate
Methotrexate Increased methotrexate toxicity due to reduced renal clearance. Moderate

Overdose & Toxicity Management

Signs of Toxicity:

  • Gastrointestinal ulceration and bleeding
  • Acute renal failure
  • Hepatic necrosis
  • Depression, lethargy
  • Ataxia or seizures (in severe cases)
  • Hypotension, shock
  • Death (in severe cases)

Emergency Treatment Protocol: There is no specific antidote for flunixin overdose. Treatment is symptomatic and supportive. Induce emesis (if oral ingestion and within 2 hours) or perform gastric lavage. Administer activated charcoal to reduce absorption. Provide intravenous fluids to maintain renal perfusion and correct dehydration. Monitor renal and hepatic function. Administer gastroprotective agents (e.g., misoprostol, omeprazole, sucralfate) to prevent or treat gastrointestinal ulceration. In severe cases, consider blood transfusion if bleeding occurs. Supportive care may include antiemetics, antacids, and nutritional support. Prognosis depends on the severity of overdose and promptness of treatment.

Food Animal Withdrawal Times

🥩 Meat: 4 days🥛 Milk: 36 days

Withdrawal times are for cattle in the US: meat 4 days, milk 36 hours (not days). For other species, consult regulatory guidelines. In horses, not intended for food production. In swine, withdrawal time is 12 days for meat (off-label).

Storage, Handling & Regulatory Information

Storage Temperature: Store at controlled room temperature 15°C to 30°C (59°F to 86°F). Protect from freezing.

Handling & Special Conditions: Protect from light. Keep container tightly closed. Do not use if precipitate forms.

Dispensing Status: Prescription Required (Rx Only)

Approval Status: FDA-approved for intravenous use in horses and cattle; for intramuscular and intravenous use in dogs. Not approved for cats, small ruminants, swine, or poultry.

Extra-Label (Off-Label) Use: In the US, flunixin meglumine is FDA-approved for use in horses, cattle, and dogs (injectable). Extra-label use in other species or routes is permitted under AMDUCA (Animal Medicinal Drug Use Clarification Act) with a valid veterinary-client-patient relationship, provided withdrawal times are extended and appropriate. In food animals, extra-label use requires careful attention to withdrawal times and may require a veterinary feed directive or prescription.

Clinical Pearls & Practice Notes

💡 Clinical Insights: Flunixin meglumine is a potent NSAID widely used in veterinary medicine for its analgesic, anti-inflammatory, and anti-endotoxic properties. It is particularly valuable in equine colic and bovine respiratory disease. In dogs, it is used for short-term pain management, but its use is limited due to the availability of safer NSAIDs. In cats, it is not approved and should be used with extreme caution due to increased risk of toxicity. Always ensure adequate hydration and monitor renal and gastrointestinal status during therapy. Do not exceed recommended doses or durations. In food animals, adhere to withdrawal times to ensure food safety. Flunixin should be used as part of a comprehensive treatment plan, including appropriate antimicrobial therapy when infection is present.

References & Literature

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