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Onsior for dogs and cats



Active ingredient



Pain relief / anti-inflammatory

What is Onsior?

Onsior is a brand name for a drug with the active ingredient robenacoxib. It is a Non-Steroidal Anti-Inflammatory Drug (NSAID), a category of drug that stops the body from producing inflammatory chemicals. In this way, Onsior lowers pain and inflammation in cats and dogs with with various conditions (e.g. joint disease, muscle pain, post-surgical pain and inflammation).

What does Onsior do?

Robenacoxib, the active ingredient in Onsior, is a Non-Steroidal Anti-Inflammatory Drug (NSAID) that targets and blocks the action of COX-2. COX-2 is a protein involved in the creation of inflammatory substances. Inflammation, fever and pain are triggered by these inflammatory substances (prostaglandins).

Onsior lowers inflammation by blocking the effects of COX-2. This manages pain in cats and dogs after surgery. Onsior also manages pain that occurs with many short-term (acute) and long-term (chronic) conditions. Thus, cats and dogs with these conditions (e.g. joint disease) can enjoy an improved quality of life when they are on Onsior. Additionally, Onsior reduces inflammation-triggered fever in cats and dogs.

What is Onsior for?

Onsior is used to manage pain and inflammation associated with a range of short-term and long-term conditions in cats and dogs. These conditions include (but are not limited to):

  • Bone or joint issues : Onsior is commonly prescribed to cats and dogs with bone/joint issues to reduce pain and inflammation. An example is degenerative joint disease (osteoarthritis). Cats and dogs with osteoarthritis can have improved mobility and comfort after starting on Onsior.
  • Muscle Pain: Onsior can alleviate pain in cats and dogs with muscle pain.
  • Post-Surgery Pain and Inflammation: Onsior is often used for postoperative inflammation and pain in cats and dogs after surgery (e.g. dental surgery, spay/neuter surgery).
  • Inflammation-induced fever: Onsior reduces inflammation-induced fever in cats and dogs.

What are the possible side effects with Onsior?

Like all medications, Onsior can have side effects. These are generally rare when the drug is used properly.

  • Gut upset: Some cats and dogs may have a gut upset. Signs include vomiting and/or diarrhoea. If there is fresh blood and/or tarry stools, sores on the gut lining (gut ulcers) may be present.
  • Sores on gut lining (gut ulcers): Prolonged use or higher doses of Onsior may cause gut ulcers.
  • Decreased Appetite: Onsior may make some cats and dogs eat less.
  • Tiredness (Lethargy): Rarely, cats and dogs may have reduced activity (lethargy). 
  • Kidney Damage: NSAIDs, including Onsior can affect kidney function. It’s crucial to monitor for excessive drinking and urination, which may indicate kidney issues.
  • Liver Damage: Liver damage may occur. Signs include vomiting, weight loss, lethargy etc. Affected pets may also have yellowed eyes, gums and/or skin (jaundice). 
  • Allergic Reactions: In very rare cases, cats and dogs may experience an allergic reaction, characterised by swelling, itching, or difficulty breathing.

Remember, not all pets will experience these side effects, and the benefits of using Onsior often outweigh the risks. However, if you notice any concerning symptoms or changes in your pet’s behaviour or health while they are taking Onsior, do inform your vet immediately. They can give advice and modify the treatment plan (if required) to ensure your pet’s safety and well-being.

Which pets is Onsior not suitable for?

Generally speaking, Onsior is not suitable for the following pets:

  • Cats and dogs allergic to Onsior, its ingredients or any other NSAID (Onsior tablets are flavoured)
  • Cats and dogs that are already on other anti-inflammatory drugs (e.g. other NSAIDs, corticosteroids).
  • Cats and dogs that are pregnant, lactating or intended for breeding
  • Dogs weighing less than 2.5kg or under 3 months of age
  • Cats weighing less than 2.5kg or under 4 months of age
  • Cats and dogs with bleeding disorders
  • Cats and dogs with dehydration, heart problems, kidney problems and liver problems

The above pets are at a greater risk of side effects from Onsior.

If your pet has any of the above issues and your vet prescribes Onsior, your vet will discuss the risks involved and the importance of close monitoring.

How to give Onsior safely

  • 1. Follow vet instructions: Generally speaking, Onsior tablets should not be broken or crushed. Onsior can be given without food or a small amount of food. However, if your pet does not tolerate Onsior on an empty stomach, consult your vet. Also, always use Onsior exactly as your vet has prescribed. This includes the right dose and frequency. Never adjust the dose on your own, even if your pet seems to be feeling better or worse. If you aren’t sure of the dose prescribed, please call your vet to confirm.
  • 2. Check with your vet if giving anything else: Your vet should be aware of other drugs your pet is on, but it’s always worth double-checking in case there’s been a miscommunication somewhere. If your pet is on supplements or non-prescription treatments you should also tell your vet when they prescribe Onsior, as they may not be suitable to be given together.

    Pets are at greater risk of side effects if they have been prescribed Onsior and they are already on other anti-inflammatory drugs (e.g. other NSAIDs, corticosteroids). If your vet wishes to switch your pet from one anti-inflammatory drug to another, your pet will be taken off the previous anti-inflammatory for a certain amount of time (a “washout period”) before being started on the next anti-inflammatory.  Therefore, you should also tell your vet about your pet’s past medications.
  • 3. Storage and Handling: Store Onsior according to the instructions on the packaging, usually in a cool and dry place. Wash your hands after giving Onsior to your pet. Make sure it’s out of reach of children and other pets. Pregnant women should not handle Onsior, as prolonged skin exposure can cause birth defects in unborn babies.
  • 4. Report any overdose to your vet immediately: If you have mistakenly given too much Onsior, inform your vet as soon as you realise the error. They may recommend blood tests, decontamination, supportive care(e.g.intravenous fluids) or monitoring, depending on the severity of the overdose.

Onsior FAQs

What is Onsior used for?

Onsior is used for cats and dogs with pain and inflammation from conditions such as joint disease. It is also often prescribed to cats and dogs with pain and inflammation from surgery.

How does Onsior make cats feel?

At proper doses, Onsior can make cats feel more comfortable and more willing to move around. The level of improvement will vary amongst cats, with some cats showing dramatic improvement.

Can I put Onsior in my cat’s food?

You can put Onsior in a small amount of your cat’s food or feed Onsior on an empty stomach.

How do I get my cat to take Onsior?

You can get your cat to take Onsior by placing the tablet in your cat’s mouth (only if your cat allows this – do not injure yourself!) Alternatively, you can get your cat to take Onsior by giving it with a small amount of food.

How many hours does Onsior last?

Onsior can last for up to 24 hours. Onsior is usually given once every 24 hours.

Onsior Datasheet

All drugs have a manufacturer’s datasheet, which gives information about the drug’s use and possible side effects. There is usually one in your Onsior box, but if you have lost it you can click on the button below to be taken on an online version.

Courses related to Onsior

Please note that the information contained herein is provided for informational purposes only. Although it has been written by a vet, we cannot consider the individual nature of your pet’s problems so it does not constitute veterinary advice. If you have questions about your pet’s medication or their health you should contact a vet, who will be able to help.

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