Flunixin Meglumine
**Flunixin meglumine** is a potent, veterinary-only non-steroidal anti-inflammatory drug (NSAID) widely used for its analgesic, anti-inflammatory, and antipyretic properties. * **Primary Uses**: It is FDA-approved in the US for horses, cattle, and swine. In horses, it is considered a gold-standard analgesic for visceral pain associated with **colic** and is also used for musculoskeletal disorders. In cattle and swine, it is primarily used to control pyrexia associated with respiratory diseases and endotoxemia. * **Extra-label Use**: While historically used in small animals (dogs), its use has been largely supplanted by newer, safer, COX-2 preferential/selective NSAIDs (e.g., carprofen, meloxicam). It is generally considered contraindicated in cats due to high sensitivity to NSAID toxicity. * **Clinical Pearl**: Flunixin is particularly noted for its ability to improve hemodynamics in animals with septic shock and its profound efficacy against visceral pain in ruminants and equines. However, it can mask behavioral and cardiopulmonary signs of endotoxemia or intestinal devitalization in colic patients.
Mechanism: Flunixin meglumine is a potent, non-selective inhibitor of the **cyclooxygenase (COX)** enzyme system. * **Mechanism**: Cell membrane phospholipids โ **Phospholipase A2** โ Arachidonic Acid โ **COX-1 / COX-2** โ Decreased production of **prostaglandins** and **thromboxanes**. * By inhibiting prostaglandin synthesis, it reduces inflammation, lowers body temperature (antipyretic), and provides significant analgesia. * Unlike some other NSAIDs, flunixin does not appreciably alter gastrointestinal motility in horses, making it highly suitable for colic management.
Dosing by species
- As an analgesic ยท 1-2 mg/kg ยท IV ยท q24h
- As an analgesic (oral paste) ยท 1-4 mg/kg ยท PO ยท once daily
- As an analgesic ยท 1-2 mg/kg ยท IV ยท q24h
- As an analgesic (oral paste) ยท 1-4 mg/kg ยท PO ยท once daily
- General ยท 0.5-2 mg/kg ยท PO or IM ยท one time daily
- For labeled indications ยท 1.1-2.2 mg/kg (1-2 mL per 100 lbs. BW) ยท slow IV ยท once a day as a single dose or divided into two doses q12h ยท up to 3 days ยท Avoid rapid IV administration
- As an analgesic ยท 1.1-2.2 mg/kg ยท IV ยท q6-12 hours ยท Recommend 72 hour milk withdrawal at this dose rate
- As an analgesic for visceral pain ยท 0.25-1 mg/kg ยท IV ยท q12-24h
- Using combination product (Resflor Gold) ยท 40 mg/kg florfenicol/2.2 mg/kg flunixin (6 mL/100 lb. B.W.) ยท SC ยท once ยท Do not administer more than 10 mL at each site. Injection should be given only in the neck.
Routes of administration
Contraindications
- Known hypersensitivity to flunixin
- Cats (generally contraindicated due to availability of safer alternatives)
- Patients with preexisting GI ulcers (e.g., Equine Gastric Ulcer Syndrome - EGUS)
- Patients with significant renal, hepatic, or hematologic diseases
- Breeding bulls (lack of reproductive safety data)
- Use to ambulate cattle intended for slaughter
Adverse effects
- Anaphylaxis (especially after rapid IV administration in horses and cattle)
- IM injection site reactions (localized swelling, induration, stiffness, sweating, and rarely clostridial myonecrosis)
- Gastrointestinal ulceration (oral and gastric ulcers, especially with prolonged use or high doses)
- Renal ischemia and nephrotoxicity (especially in dehydrated patients, dogs, and birds)
- Hematochezia and hematuria (reported in cattle treated > 3 days)
- Hypoproteinemia and hematologic abnormalities
Drug interactions
- Aspirin ยท May decrease plasma levels of flunixin and increase the likelihood of GI adverse effects (blood loss)
- Cyclosporine ยท May increase cyclosporine blood levels and increase the risk for nephrotoxicity
- Digoxin ยท May increase serum levels of digoxin; use with caution in severe cardiac failure
- Enrofloxacin ยท Increases AUC and elimination half-life of both flunixin and enrofloxacin in dogs
- Furosemide & other diuretics ยท May reduce the saluretic and diuretic effects of the diuretic
- Methotrexate ยท Serious toxicity has occurred with concomitant use; use together with extreme caution
- Nephrotoxic agents (e.g., aminoglycosides, amphotericin B) ยท Increased risk of synergistic nephrotoxicity
- Probenecid ยท May cause a significant increase in serum levels and half-life of flunixin
- Warfarin ยท May increase the risk for bleeding
Monitoring
- Analgesic, anti-inflammatory, and antipyretic efficacy
- Gastrointestinal effects (especially in dogs and horses)
- CBCs and occult blood in feces with chronic use in horses
- Renal parameters (BUN, Creatinine, USG) in susceptible species or dehydrated patients
Overdose
Acute overdosage should be handled by using established protocols of emptying the gut (if oral ingestion and practical/possible) and treating the patient supportively. * **Gastric Ulceration**: A distinct possibility in horses that have received overdoses. Consider using prophylactic anti-ulcer medications (e.g., omeprazole) in overdosed horses. * **Renal Protection**: Ensure adequate hydration and monitor renal values closely.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturerโs current label.