Robenacoxib in Cats

Robenacoxib is a prescription NSAID used in cats to reduce pain and inflammation. In the United States, the labeled feline product is Onsior, and it is FDA-approved for short-term control of postoperative pain and inflammation associated with orthopedic surgery, ovariohysterectomy, and castration in cats that are at least 4 months old. It is available as a 6 mg tablet for cats and as a veterinary injection, and treatment is limited to a maximum of 3 total doses over 3 days.

This medication is often chosen when a cat needs short-term pain relief around surgery. Your vet may give the first dose before the procedure, then continue with tablets or another injection afterward. While robenacoxib is sometimes discussed for other painful conditions, any use outside the label should be decided by your vet based on your cat’s age, hydration status, kidney function, liver health, and overall risk profile.

For pet parents, the key point is that robenacoxib is not an over-the-counter pain reliever and should never be replaced with human NSAIDs like ibuprofen or naproxen. Cats are especially sensitive to medication errors. Even when a drug is labeled for cats, safe use depends on the right patient, the right dose, and close attention to appetite, energy level, vomiting, stool changes, and urination.

Robenacoxib works by blocking cyclooxygenase-2, usually shortened to COX-2. This enzyme helps the body produce inflammatory chemicals that contribute to pain, swelling, and fever. Because robenacoxib is COX-2 selective, it is designed to target inflammation more than some older NSAIDs, while having less effect on COX-1, an enzyme involved in stomach protection, kidney blood flow, and normal clotting support.

That selectivity matters, but it does not make the drug risk-free. At higher exposures or in vulnerable cats, NSAIDs can still affect the stomach, intestines, kidneys, and liver. This is one reason your vet may recommend baseline bloodwork or extra caution in cats that are dehydrated, very young, elderly, or already dealing with kidney, liver, heart, or gastrointestinal disease.

Robenacoxib has a fairly rapid onset of action in cats, with label information noting effects within about 30 minutes in an inflammation model. The oral tablets may be given with or without food, but food can reduce absorption for some NSAIDs, including robenacoxib. In practice, your vet may balance that detail against your cat’s tolerance. If a cat vomits on an empty stomach, giving future doses with a small meal may be the more practical option.

The most common side effects reported with robenacoxib are gastrointestinal and appetite-related. Pet parents may notice decreased appetite, vomiting, diarrhea, lethargy, or a lower activity level. Some cats also develop irritation, bruising, or bleeding concerns around the incision after surgery. Mild stomach upset can happen, but any persistent vomiting, repeated diarrhea, or refusal to eat should prompt a call to your vet.

More serious reactions are less common but more important. NSAIDs can contribute to stomach ulceration, intestinal bleeding, kidney injury, and liver problems. Warning signs include black or tarry stool, blood in vomit, yellowing of the gums or skin, unusual thirst, changes in urination, weakness, wobbliness, seizures, or marked depression. If these signs appear, stop the medication and contact your vet right away.

Cats at higher risk include those that are dehydrated, have pre-existing kidney or liver disease, have a history of NSAID intolerance, or are taking other medications that stress the kidneys or stomach. Because appetite loss can be an early clue that a cat is not tolerating the drug well, monitoring food intake during treatment is especially important. See your vet immediately if your cat becomes very lethargic, stops eating, vomits repeatedly, or seems painful despite treatment.

In U.S. cats, labeled oral dosing is 1 mg/kg by mouth once daily for up to 3 days, using 6 mg tablets. The tablets are approved for cats at least 4 months old and at least 5.5 pounds. The dosing chart on the label gives 1 whole 6 mg tablet once daily for cats weighing 5.5 to 13.2 pounds and 2 whole tablets once daily for cats weighing 13.3 to 26.4 pounds. The tablets are not scored and should not be broken.

The injectable form is dosed differently from the tablets. For cats, the labeled injection dose is 2 mg/kg subcutaneously once daily for up to 3 days. The first dose is commonly given about 30 minutes before surgery, and later doses may be continued as injections or switched to tablets in eligible cats. Because the tablet and injection doses are different, pet parents should never assume they are interchangeable without clear instructions from your vet.

Give robenacoxib exactly as prescribed. It may be given with or without food. If your cat vomits after getting it on an empty stomach, ask your vet whether future doses should be given with a small meal. Do not double up if you miss a dose unless your vet specifically tells you to do so. This medication is intended for short-term use, so if your cat still seems painful after the prescribed course, contact your vet rather than extending treatment on your own.

The most important interaction rule is that robenacoxib should not be given with another NSAID or with a corticosteroid unless your vet has a very specific reason and monitoring plan. Combining these drugs can sharply increase the risk of stomach ulceration, intestinal bleeding, kidney injury, and other complications. That means pet parents should tell your vet about every medication and supplement a cat is taking, including aspirin, meloxicam, prednisolone, dexamethasone, and over-the-counter products.

Extra caution is also needed with drugs that can affect kidney perfusion or hydration status, such as diuretics, some blood pressure medications, and certain anesthetic or sedative plans. Cats that are dehydrated or have poor circulation are more vulnerable to NSAID-related kidney problems. This is one reason fluid therapy is often recommended around surgery when NSAIDs are used.

If your cat is on long-term medications for chronic disease, ask your vet whether robenacoxib changes the monitoring plan. In some cases, your vet may recommend baseline bloodwork, urinalysis, or a different pain-control strategy. The safest approach is to avoid mixing pain medications at home unless your vet has clearly written out the plan.