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Robenacoxib is a prescription anti-inflammatory tablet for cats. In the United States, the Onsior tablet label covers control of postoperative pain and inflammation after orthopedic surgery, ovariohysterectomy (spay) and castration. It is labeled for cats at least four months old and at least 5.5 lb (2.5 kg), at 1 mg/kg (0.45 mg/lb) by mouth once daily, for no more than three days. Anything beyond that, or any use outside those indications, is a decision for the prescribing veterinarian.
This guide reflects U.S. labeling and U.S. Food and Drug Administration (FDA) guidance as checked on October 9, 2026. Doses, approvals and product availability differ in other countries and can change, so confirm them with a local veterinarian or regulator.
What robenacoxib is
Robenacoxib belongs to the coxib class of nonsteroidal anti-inflammatory drugs (NSAIDs). Like other NSAIDs, it reduces inflammation and pain, but it is not a sedative and does not treat the underlying cause of a problem. It is sold under the brand name Onsior in the United States, and tablets are prescription-only, so a licensed veterinarian must authorize them.
What the U.S. label covers
The FDA-approved tablet indications are narrow: postoperative pain and inflammation associated with three procedures, namely orthopedic surgery, ovariohysterectomy and castration. The label does not establish that robenacoxib is approved in the U.S. for every cause of feline pain, such as arthritis flares, dental pain or injury. Using it for those purposes is an off-label decision that belongs to the veterinarian, who may weigh other options.
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Eligibility for tablets
- Age: at least four months old.
- Weight: at least 5.5 lb (2.5 kg).
- Not evaluated in: cats under four months, cats under 5.5 lb, cats used for breeding, and pregnant or lactating cats.
- Contraindicated in: cats with known hypersensitivity to robenacoxib or known intolerance to NSAIDs.
Dosage and duration
The labeled dose is 0.45 mg/lb (1 mg/kg) by mouth once daily, with a maximum of three days of treatment. The label directs use of the lowest effective dose for the shortest duration consistent with the individual cat’s response. The tablet chart works in whole tablets, and the 6 mg tablets are not scored and should not be broken.
| Cat’s weight (U.S. label chart) | Labeled tablet amount, once daily |
|---|---|
| 5.5–13.2 lb (2.5–6 kg) | One 6 mg tablet |
| 13.3–26.4 lb (6.1–12 kg) | Two whole 6 mg tablets |
These figures are the printed label directions, not a calculation for your cat. Cats outside the weight bands in this chart need veterinary direction, and owners should never split a tablet to fit a dose.
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Before the first dose
The label requires a veterinary history and physical examination before NSAID therapy, plus appropriate laboratory tests to establish hematological and serum biochemical baseline data. Dehydrated cats, cats on diuretics, and cats with existing kidney, heart or liver dysfunction may face a higher risk of adverse events. The label recommends perioperative fluid therapy when an NSAID is used, to reduce the risk of kidney complications. Whether your cat has any of these conditions is for the veterinary team to establish, not for an owner to infer from symptoms at home.
Side effects and what to do
The owner information in the U.S. tablet label lists these signs of possible intolerance:
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- Vomiting or diarrhea
- Decreased appetite
- Dark or tarry stools
- Increased water consumption or increased urination
- Signs of anemia
- Yellowing of the gums, skin or whites of the eyes (jaundice)
- Lethargy or incoordination
- Seizures or behavioral changes
If any of these appear, stop the tablets and contact the veterinarian immediately. The label also says to stop if appetite drops or the cat becomes lethargic. Do not wait to see whether the sign passes.
Medicines to avoid combining
Do not give Onsior tablets or injection together with another oral or injectable NSAID, or with a corticosteroid. Tell the veterinarian about every medication, supplement and prescription the cat already takes before the first dose, because the combination risk applies to other anti-inflammatory drugs as well.
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Limits on repeating or extending treatment
FDA consumer guidance on pain relievers for pets states that more than three doses of robenacoxib in cats have not been shown to be safe. Do not prolong, restart or adjust a course because the cat seems to be in pain or seems better. Any further treatment needs a new veterinary assessment.
Tablets and the injection are different products
Onsior also has an injectable form, given by a veterinary team under its own label. The injection is not interchangeable with the tablets on a milligram-for-milligram or dose-for-dose basis, and it has its own labeled dose. The injection label times the first dose before surgery, and in eligible cats later doses may be given as tablets, within a total maximum of three doses over three days. Those timing and switching decisions belong to the veterinary team.
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Generic robenacoxib
On January 9, 2026, the FDA announced approval of the first generic robenacoxib tablet for the same postoperative indications in cats at least four months old and 5.5 lb. The FDA says the generic contains the same active ingredient as Onsior, is bioequivalent to the brand-name product, is prescription-only, and may be given for up to three days. The sponsor named in that notice is ZyVet Animal Health, Inc. On March 9, 2026, the FDA announced approval of the first generic robenacoxib injectable product for postoperative pain and inflammation in dogs and cats.
Where the evidence stops
The official sources reviewed here establish labeled doses, eligibility, warnings and approval status. They do not provide an effectiveness percentage or an adverse-event rate for cats, so this article makes no such claim. Ask your veterinarian about the expected response and what monitoring to plan for your cat’s procedure or condition.
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