Flunixin meglumine is a nonsteroidal anti-inflammatory drug (NSAID) used in veterinary medicine to control pain, inflammation, and fever in horses, cattle, and swine. It’s one of the most widely used medications in equine practice, particularly for managing colic, and plays a significant role in cattle health as well. If you’ve encountered this drug at the barn or on the farm, here’s what you need to know about how it works, when it’s used, and what to watch out for.
How Flunixin Meglumine Works
Like human NSAIDs such as ibuprofen, flunixin meglumine works by blocking enzymes called COX-1 and COX-2. These enzymes produce prostaglandins, which are chemical messengers that trigger pain, inflammation, and fever. By suppressing prostaglandin production, the drug reduces all three.
Flunixin is classified as a nonselective NSAID, meaning it blocks both COX-1 and COX-2 in roughly equal measure. This matters because COX-1 also plays a protective role in the body, maintaining the lining of the stomach and intestines and supporting normal kidney blood flow. Blocking it is what gives the drug its side effects, which mirror those of nonselective NSAIDs in human medicine.
Approved Uses in Horses
Flunixin meglumine is FDA-approved in horses for two main purposes: relieving inflammation and pain from musculoskeletal disorders (like lameness and joint injuries), and alleviating the visceral pain associated with colic. It is, by a wide margin, the most commonly used drug for colic pain and has become a go-to for veterinarians and horse owners alike.
For colic specifically, the standard dose is 0.5 mg per pound of body weight, given intravenously for the fastest relief. For musculoskeletal issues, the same dose can be given intravenously or intramuscularly, once daily for up to five days.
The Colic Question
While flunixin is effective at controlling colic pain, its role in serious surgical colic cases is more complicated than many horse owners realize. The drug does not treat the underlying cause of colic. It manages symptoms. In horses with severe intestinal injuries, such as a strangulating obstruction where blood flow to a section of gut is cut off, flunixin can actually increase intestinal permeability, making it harder for damaged gut lining to heal and allowing bacterial toxins to leak into the bloodstream.
Veterinarians have long used a lower “anti-endotoxic” dose (roughly a quarter of the standard dose) with the idea that it could fight the effects of bacterial toxins without masking the clinical signs that help determine whether surgery is needed. However, there is no strong evidence that flunixin at any dose reduces complication or mortality rates in severe colic cases. This has led some veterinary researchers to argue that the drug’s reputation as indispensable for every colicking horse deserves more scrutiny.
None of this means you should avoid giving flunixin for colic. It remains a highly effective pain reliever for simple, non-surgical colic episodes. The key is that pain control should not replace veterinary evaluation, especially if symptoms persist or worsen after the drug is given.
Approved Uses in Cattle
In cattle, flunixin meglumine is approved for controlling fever associated with bovine respiratory disease and endotoxemia (a dangerous condition where bacterial toxins flood the bloodstream). It’s also approved for managing inflammation in endotoxemia and as a single-dose treatment during acute mastitis.
The cattle dose ranges from 1.1 to 2.2 mg/kg of body weight, given by slow intravenous injection once daily or split into two doses 12 hours apart, for up to three days. For acute mastitis, a single intravenous dose of 2.2 mg/kg is used.
Transdermal Option for Cattle
A newer formulation, sold under the brand name Banamine Transdermal, is applied as a liquid strip along the animal’s back and absorbed through the skin. This is notable because it is currently the only NSAID approved to control pain in a food-producing animal. It was specifically approved for managing pain from foot rot in cattle, providing relief even before the antibiotic treating the underlying infection takes full effect. The pour-on application also eliminates the risks associated with injections, including tissue damage at the injection site that can cause carcass defects.
Withdrawal Periods for Food Animals
If you raise cattle for meat or milk, withdrawal times are critical. When flunixin is administered according to label instructions, the withdrawal time for milk is 36 hours. The marker residue that regulators test for in milk is a metabolite of flunixin, and the tolerance limit is extremely low (2 parts per billion). Meat withdrawal times vary by formulation and route, so following the label for your specific product is essential to avoid violative residues that could result in regulatory action.
Side Effects and Risks
At the recommended dose and duration, flunixin meglumine is generally well tolerated. Studies in neonatal foals found no significant differences in blood work between foals given the standard dose and those given saline. However, foals given six times the recommended dose developed significant gastrointestinal ulceration and damage to the cecum (a key part of the horse’s hindgut).
The primary risks with flunixin are the same as with other nonselective NSAIDs:
- Gastrointestinal damage: Stomach and colon ulceration, particularly with prolonged use or higher-than-recommended doses. The right dorsal colon in horses is especially vulnerable.
- Kidney stress: Because the drug reduces blood flow to the kidneys by blocking protective prostaglandins, animals that are dehydrated or have existing kidney or liver disease are at higher risk of kidney damage.
- Protein loss: Extended use can lead to drops in blood protein levels, a sign of gut lining damage that allows protein to leak out.
Conditions that reduce the body’s ability to clear the drug, including dehydration, kidney disease, and liver disease, make toxicity more likely even at standard doses.
Drug Interactions to Avoid
One of the most important safety rules with flunixin is to never combine it with another NSAID, a practice known as “stacking.” Giving two different NSAIDs at their recommended doses is essentially the same as doubling the dose of one, and the toxic effects add up quickly. In one study, horses given both phenylbutazone and flunixin at standard doses for just five days showed significant drops in plasma protein and increased rates of gastric ulceration compared to horses on either drug alone or a placebo.
Combining flunixin with certain antibiotics that are hard on the kidneys, such as aminoglycosides or oxytetracycline, also raises the risk of kidney damage. If your horse or cow is on multiple medications, your veterinarian needs to know about all of them to avoid dangerous combinations.