Pain Killers in Pets: All You Need to Know About NSAIDs

Pain killers in pets are crucial in many conditions to help them remain comfortable.  In this article I run through all you need to know about the most common ant-inflammatories in dogs and cats, the non-steroidal anti-inflammatory drugs (NSAIDs).


Our non-steroidal anti-inflammatory drugs, which are also known as non-steroidals and NSAIDs, are the most commonly prescribed pain killer in dogs and cats.  They are used as pain killers, to reduce inflammation and swelling and also to reduce a high temperature.  While there are many different options for pain killers in dogs and cats, none of the others them have all of these effects.

The most common uses of non-steroidals in dogs and cats are the management of chronic pain conditions such as arthritis as well as for pain relief following injury or surgery.  These drugs also have some anti-cancer effects, an area of their use where research is ongoing and recommendations changing.

There are many different drugs within the non-steroidal anti-inflammatory class including carprofen, meloxicam, firoxocib and mavacoxib to name but a few.  These are then sold under many trade names including Rimadyl, Metacam, Previcox and Trocoxil.

How do they work?

Non-steroidal anti-inflammatories work by stopping the enzymes from working that make pro-inflammatory chemical know as prostaglandins.  These prostaglandins cause swelling, an increase in temperature as well as amplifying the pain signal sent to the brain by the local nerves.  The enzymes that are blocked are known as the COX enzymes, specifically COX 1 and COX 2.  COX 1 is actually responsible for the function of normal, healthy body processes.  These include maintaining the intestinal lining and ensuring adequate blood flow to the kidneys.

Blocking COX 1 therefore can result in upsetting normal body functions and so potential cause the side-effects I discuss a little later.  COX 2 however is the enzyme that goes into action whenever damage takes place and results in the production of these inflammatory prostaglandins resulting in pain and inflammation.

This is important to know because we want to make sure we reduce pain and inflammation while at the same time reducing the risk of side-effects.  In other words we want our drugs to block COX 2 and not COX 1.  Most readily accessible human NSAIDs do not do this in dogs and cats and as a result side effects are really common when given to our pets.

Our pet specific anti-inflammatories however are considered COX 2 preferential or COX 1 sparing meaning that they have a more specific action on the things we want, while at the same time having less effect on normal body function.  This difference though is species specific.  An example would be that carprofen is much more COX 2 preferential in dogs compared to cats.

Side effects

This brings us to the potential side effects of these drugs.  As you can imagine from the way these work, the most common side effect is mild gastrointestinal upset resulting in diarrhea and vomiting as well as lethargy and inappetence.  This appears to happen in 2-9% of patients, with reports varying slightly.  If treatment is continued despite vomiting or diarrhea being present then there is the risk of intestinal ulceration developing which may progress to full perforation.

Vomiting or diarrhoea happens in about 5% of pets who take anti-inflammatories, what other side effects do you need to know about?

It's also worth noting that the newer drugs haven't consistently been shown to be significantly less likely to produce side-effects that those that have been around for some time.  Although certain individuals definitely do seem to do well on a particular non-steroidal when another once caused side-effects.  This seems very much to relate to the individual rather than the specific drug.

Other side effects do happen although are considered rare.  Dogs are more prone to liver damage which occurs in around 1-in-2000 patients and is generally reversible so long as it is detected early and the damage is not too severe.

Cats on the other hand are more prone to kidney damage.  While this can happen following a single injection, kidney damage is very rare when our NSAIDs are used appropriately.  Interestingly though there are a couple of reports of cats with existing kidney disease that also had arthritis doing better when given meloxicam compared to those not treated with this drug.

An even smaller percentage of patients will develop clotting problems as these drugs can affect platelet function and so reduce the ability of the blood to clot.

For a full run-down of the safety of metacam in cats and pain killer safety in dogs make sure you check out these articles which discuss how to reduce the risk of the side-effects happening in your pet.  One of the big ones is to give these drugs with food which may reduce the likelihood of intestinal upset.


Any patient being given these drugs should be monitored at home for side-effects and if there are any concerns then they should be stopped and you vet consulted.  As well as vomiting and diarrhea, symptoms to look out for include a reduced appetite, stopping drinking or drinking more, lethargy, weakness, yellow or white gums, urinating a lot and weight loss.

As well as looking out for these symptoms it is advisable for any dog or cat taking non-steroidal anti-inflammatories to have blood and urine testing carried out on a regular basis.  While this will vary between patients a suggested schedule might include a pre-treatment sample, another test run 2-4 weeks later and then repeat testing every 3-6 months after this.  Running these tests may help pick up any kidney or liver damage early, minimizing the chance of any ongoing effects.

regular blood testing can pick up side-effects before they become serious

These drugs should also be used cautiously in patients with pre-existing chronic disease such as liver and kidney disease as well as those patients on a number of drugs including ACE inhibitors, aspirin, steroids, diuretics and phenobarbitone.  It can be difficult in some cases to balance all the needs of our senior patients, especially those with multiple conditions.

I believe though that where a patient is in chronic pain, such as with arthritis, it is not acceptable to ignore this because of a slight increase in risk of side-effects.  There may be other appropriate drug options but quality of life should not be ignored.  I discuss this in more detail in my video on the drug treatment of arthritis.

I hope this helps you better understand this commonly used class of drugs and it helps ensure your pet remains pain-free.  If you have any questions please ask them below and also sign up to my newsletter so you don't miss out on future articles dedicated to helping your pet.

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