Onsior (Robenacoxib) for Cats: A Medication for Pain After Surgery

When it comes to managing pain in cats, the options for pain medications are limited. Onsior (robenacoxib) for cats is a nonsteroidal anti-inflammatory drug (NSAID) that is approved by the FDA to manage pain in cats in certain situations.

In this article, we’ll cover how Onsior works, what types of pain it’s used for, and the potential adverse effects and safety concerns associated with the medication.

Onsior for cats at a glance

What is Onsior for cats, and how does it work?

Onsior is the brand-name version of the medication robenacoxib. Onsior is an NSAID that is FDA approved to relieve pain and inflammation in cats after surgery. It is the first NSAID that is FDA approved for use in cats.

Onsior works by blocking certain enzymes (proteins that cause chemical reactions) that lead to inflammation. It is considered safer for cats than other NSAIDs because it is much more selective in which enzymes it blocks. As a result, Onsior is less likely to cause NSAID side effects that cats are especially sensitive to.

What is Onsior used for in cats?

Onsior for cats is used to treat pain and inflammation after orthopedic surgery and spay or neuter surgery. Onsior for cats is FDA approved for up to 3 days after these surgical procedures.

Options to manage pain are very limited for cats. Onsior is the only NSAID that is FDA approved for use in cats. It’s often considered the safest choice for pain related to short-term issues, including broken bones and other injuries.

Off-label uses for Onsior include managing acute pain for up to 6 days and managing chronic pain from arthritis for up to 1 month. According to studies, cats with arthritis did well taking Onsior for 1 month, including some cats with chronic kidney disease. No negative side effects or changes to lab work (including liver and kidney values) were detected in these cases.

As with any NSAID, cat parents should weigh the potential risks and benefits of long-term use of Onsior. The potential risks and benefits differ for each cat, so it’s important to talk to your vet about the medication.

If your cat is prescribed Onsior for longer-term use, follow your veterinarian’s directions carefully. Their directions may vary significantly from the instructions on the label.

How is Onsior given to cats, and what is the standard dosage?

According to the manufacturer’s instructions, the standard Onsior dosage for a cat who weighs 5.5 lbs to 13.2 lbs is one 6 mg tablet daily. For cats weighing 13.3 lbs or more, the dosage is two 6 mg tablets daily.

Additional dosage-related information includes:

• Onsior for cats is FDA approved to be used once daily for up to 3 days.

• Onsior flavored tablets are not scored and should not be split in half.

• Onsior is approved to be used in cats who weigh more than 5.5 lbs, since the tablets can’t be separated into smaller doses for cats who weigh less.

• Onsior for cats can be taken with or without food. But giving your cat the medication without food may increase its absorption.

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Onsior for cats also comes in an injectable form. But this form of the medication is used only in veterinary hospitals. Injectable Onsior is typically given before surgery to reduce pain after surgery.

What are the common side effects of Onsior in cats?

The most common side effects of Onsior for cats include:

• Decreased appetite

• Soft stool

• Vomiting

• Lack of energy

These side effects are generally temporary and go away after your cat stops taking the medication.

What are the most serious risks of Onsior for cats?

Although Onsior is generally considered safer for short-term use in cats compared with other NSAIDs, there is still a risk for serious effects. The most common adverse side effects reported with Onsior, and other NSAIDs, are:

• Stomach upset

• Stomach ulcers

• Kidney damage

• Liver damage

• Bleeding disorders

Very rare, but potential, side effects of Onsior for cats include:

• Bloody urine

• Breathing problems

• Incoordination

• Death

These rare side effects are thought to be related to kidney failure. Onsior side effects are more likely in cats who are:

• Generally sick

• Dehydrated

• Taking a diuretic medication

• Diagnosed with preexisting liver, heart, or kidney problems

Does Onsior interact with other cat medications?

Onsior for cats should not be given with other NSAIDs or with steroids, including:

• Angiotensin-converting enzyme (ACE) inhibitors like enalapril

• Baby aspirin

• Budesonide

• Depo-Medrol injections

• Diuretics

• Fluconazole

• Methotrexate

• Other NSAIDs like meloxicam

• Prednisolone and other steroids

Before you give Onsior to your cat, tell your vet about over-the-counter medications and supplements your cat takes on a regular basis.

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Written by:

Sarah J. Wooten, DVM, CVJ

Dr. Sarah Wooten, DVM, CVJ, is a well-known international influencer in the veterinary and animal healthcare spaces. She has 16 years of experience in private practice and more than 15 years experience in veterinary media work.

Edited by:

Renée Fabian, MA

Renée Fabian is the senior pet health editor at GoodRx. She’s worked for nearly 10 years as a journalist and editor across a wide range of health and well-being topics.

Reviewed by:

Ghanasyam Bey, DVM

Ghanasyam Bey, DVM, is from Cleveland, Ohio, and attended Princeton University for undergraduate studies. After a year of biology research at Duke University, he attended Ohio State College of Veterinary Medicine.

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