Onsior (Robenacoxib) for Cats: Uses, Dosage & Safety

This information is for educational purposes only. Never give your pet any medication without your veterinarian's guidance. Dosing, frequency, and safety depend on your pet's specific health profile.

Onsior is the brand name for robenacoxib, a prescription nonsteroidal anti-inflammatory drug, or NSAID, made for veterinary use. In cats, it is used to reduce pain and inflammation for a short, defined period under your vet's supervision. It belongs to the coxib group of NSAIDs, which are designed to be more selective for the COX-2 enzyme involved in inflammation.

In the United States, Onsior is one of the very few NSAIDs specifically approved for cats. That matters because cats process many medications differently than dogs and people do. NSAIDs can be helpful, but they also carry real risks, especially involving the kidneys, stomach, intestines, and liver if used in the wrong patient or for too long.

For cats, Onsior is not a medication pet parents should keep using on their own after the prescribed course ends. The FDA-approved labeling limits feline use to a maximum of 3 total doses over 3 days, and the tablets are only labeled for cats 4 months and older that weigh at least 5.5 pounds. Your vet may choose tablets, an injection, or a short combination of both depending on the situation.

In U.S. cats, Onsior is primarily labeled for the control of postoperative pain and inflammation associated with orthopedic surgery, ovariohysterectomy (spay), and castration (neuter). The first dose is often given around the time of surgery, and your cat may go home with additional doses to complete the short course.

Your vet may also discuss robenacoxib when a cat has acute pain linked to inflammation, such as some musculoskeletal injuries, but whether that is appropriate depends on the cat's age, hydration, kidney values, appetite, and other medications. Cats with vomiting, dehydration, low blood pressure, kidney disease, or a history of NSAID sensitivity may need a different plan.

Onsior is not a long-term daily pain medication for cats in the U.S. If your cat has ongoing pain from arthritis, dental disease, injury, or another chronic condition, your vet may recommend a different strategy. That may include other pain medications, joint support, environmental changes, weight management, or a multimodal plan rather than extending Onsior beyond the labeled short course.

Always follow the exact instructions from your vet. For cats, the FDA-approved oral tablet is a 6 mg tablet used in cats 4 months of age or older and at least 5.5 lb (2.5 kg). The labeled dosing table is 1 whole 6 mg tablet once daily for cats weighing 5.5 to 13.2 lb (2.5 to 6 kg) and 2 whole 6 mg tablets once daily for cats weighing 13.3 to 26.4 lb (6.1 to 12 kg). Tablets are not scored and should not be broken.

Onsior tablets may be given with or without food, though some vets prefer giving medications with a small meal if stomach upset is a concern. In surgical patients, the first dose is commonly given about 30 minutes before surgery with pre-anesthetic medications. After that, your cat may receive tablets at home, but the total course should not exceed 3 total doses over 3 days, including any injection given at the hospital.

Do not increase the dose, give extra days, or combine it with leftover pain medicine unless your vet specifically tells you to. If you miss a dose, call your vet for guidance rather than doubling the next one. If your cat is underweight, very young, dehydrated, not eating, or has kidney, liver, heart, or stomach concerns, your vet may decide Onsior is not the right fit or may recommend closer monitoring.

Many cats tolerate a short Onsior course well, but side effects can happen. Mild problems may include vomiting, soft stool or diarrhea, decreased appetite, or lower energy. Even mild signs matter with NSAIDs, because they can be the first clue that the stomach, intestines, kidneys, or liver are not handling the medication well.

Stop the medication and contact your vet promptly if your cat becomes lethargic, stops eating, vomits repeatedly, has diarrhea that continues, seems painful despite treatment, or acts unusually weak or unsteady. More serious warning signs include black or bloody stool, collapse, pale gums, increased thirst, changes in urination, yellowing of the eyes or gums, or seizures. These are not common, but they are urgent.

Cats are especially sensitive to dosing errors and prolonged NSAID exposure. The package insert also notes that robenacoxib can prolong the QT interval, and neurologic signs such as ataxia, nystagmus, and seizures have been reported. See your vet immediately if your cat has any severe reaction or if another pet or child accidentally gets into the medication.

Onsior should not be given at the same time as other NSAIDs or corticosteroids unless your vet has created a specific plan. That includes medications such as meloxicam, carprofen, aspirin, prednisone, prednisolone, and dexamethasone. Combining anti-inflammatory drugs raises the risk of stomach ulceration, intestinal bleeding, kidney injury, and other serious complications.

Caution is also needed with drugs that may affect the kidneys, hydration status, blood pressure, or protein binding. Depending on your cat's case, your vet may review diuretics, ACE inhibitors, some heart medications, anticonvulsants, and behavior medications before prescribing Onsior. The label also advises against combining robenacoxib with medications known to prolong the QT interval.

Before your cat starts Onsior, tell your vet about every medication, supplement, flea/tick product, and over-the-counter item your cat receives. That includes appetite stimulants, anti-nausea drugs, pain medications, inhalers, and supplements. If your cat recently had another NSAID or a steroid, ask your vet whether a washout period or a different pain-control option is safer.