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Flunixin Meglumine for Horses

By Barbara Forney, VMD

Last reviewed: 7/13/2022

Commonly prescribed for: Pain Relief to Treat Colic

Species: Horses

Therapeutic Class: Nonsteroidal Anti-inflammatory Drug (NSAID) and Cyclooxygenase Inhibitor

Basic Information

Flunixin meglumine is a nonsteroidal anti-inflammatory drug (NSAID) and cyclooxygenase inhibitor. It is a potent analgesic, antipyretic, and anti-inflammatory. NSAIDs work by inhibiting the body's production of prostaglandins and other chemicals that stimulate the body's inflammatory response. Some of these actions may be dose-dependent. NSAIDs are quickly absorbed into the blood stream; pain relief and fever reduction usually starts within one to two hours.


Flunixin meglumine commonly is used for pain relief to treat colic. It is used for protection from septic/endotoxic shock due to any gastrointestinal (GI) insult either post surgical or medical such as in cases of peritonitis or diarrhea. Flunixin is used commonly as an anti-inflammatory to treat painful conditions of the eye including corneal ulcers, uveitis, conjunctivitis, and before and after eye surgery. It may be used to reduce or control fevers due to viral or bacterial infections. Although flunixin can be used to treat arthritis, there are other NSAIDs that are prescribed more commonly for this purpose.

Flunixin may be given IV, IM, or orally.

Flunixin Meglumine Side Effects

  • The most-common side effects include GI ulceration, especially of the stomach and large colon.
  • Rare side-effects include kidney damage and bleeding disorders.
  • Allergic reactions are rare but have been reported.


  • GI side-effects such as ulcers are more likely to occur with prolonged oral dosing. Renal problems are more likely to occur in the dehydrated or debilitated horse. NSAIDS should be avoided or very carefully monitored in horses with liver disease, kidney disease, or those prone to GI ulcers.
  • Side effects from NSAID use are more common with phenylbutazone than with flunixin.
  • Flunixin should be used with caution in the pregnant or nursing mare. No adverse effect on sperm production has been reported.
  • Flunixin is used in foals, but it should be used with particular caution to avoid GI ulceration and maintain kidney function. Premature foals, septicemic foals, foals with questionable kidney or liver function, and foals with diarrhea require careful monitoring. Drugs to protect the GI tract such as omeprazole, cimetidine, or sucralfate are frequently used with flunixin.
  • Pony breeds may be more susceptible to side effects from NSAIDs than horses. When flunixin is used in ponies, it should be used with caution and at the lowest effective dose.
  • Older horses and especially those with decreased kidney or liver function may be more at risk for side effects. When flunixin is used in older horses it should be used carefully and at the lowest effective dose.
  • Injectable flunixin can be given IM, but injection site reactions, including localized pain, swelling, muscle inflammation or damage sometimes occur.
  • Some veterinarians and many horse owners, particularly those involved in showing, use more than one NSAID in combination, for example, flunixin and phenylbutazone given together. Although there is little experimental evidence to support this practice, the theory is that different NSAIDs may act differently on different body systems. Particular care needs to be taken in this situation to avoid additive toxicity.
  • Drug Interactions
  • Avoid combining with other anti-inflammatory drugs that tend to cause GI ulcers, such as corticosteroids and other NSAIDs.
  • Use with caution with aminoglycoside antibiotics such as gentamicin and amikacin and oral anticoagulants such as warfarin and other coumarin derivatives.


  • A single miscalculated dose is not likely to produce toxicity. Experimentally it has taken three to five times the normal dose over multiple days to produce toxicity.
  • Overdose with flunixin will increase the likelihood and severity of the mentioned side effects. Early signs of toxicity include loss of appetite and depression.
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