Loxicom, Metacam and so on and so on. There are many non-steroid anti-inflammatory medications that are commonly used to treat pain and inflammation in our dogs and cats but they can cause side effects, including tummy upsets, vomiting, diarrhoea, gastric ulceration, kidney and liver issues, and loss of appetite.

But why do they do this? Let me try and explain.

Pain and inflammation occur in arthritic animals because of complicated chemical pathways that result in the synthesis of a compound called prostaglandin. In this discussion, therefore, prostaglandins are bad. They are most definitely the boys to be avoided.

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The two major pathways that lead to the production of prostaglandins in dogs are called Cox 1 and Cox 2, with the latter being the most important route.

Imagine, for a moment, that Cox 1 and Cox 2 are like the A8 and the M8 respectively, and that traffic that gains access to the car park at Edinburgh Castle causes prostaglandins to be released. (Indeed, I can hear you murmur a little over this one, so I suggest you go back and read it again and bear with me.)

Most of the prescribed non-steroid anti-inflammatories (NSAIs) that we use in dogs selectively block Cox 2 (or the M8), but this can obviously cause problems, and, sometimes, madness.

Chemicals used to tackle pain in dogs with arthritis can have major effects on other systems in the animal's body.Chemicals used to tackle pain in dogs with arthritis can have major effects on other systems in the animal's body. (Image: Diana Parkhouse/Unsplash.com) Not all traffic on the M8, for example, is bound for Edinburgh, so Cox 2 inhibitors can create chaos in other bodily systems, so that a variety of side-effects, such as vomiting, diarrhoea or bleeding can occur.

Different NSAIs block the pathway at specific sites so that, after a while, traffic becomes accustomed to them and starts to jump from the M8 onto the A8. You can see then that vehicles can begin to trickle into Edinburgh, and the efficacy of the drug is diminished.

his process explains why occasionally changing the NSAI, and therefore altering where the pathways are inhibited, can improve clinical signs.

But the bottom line is that stopping all traffic from getting to Edinburgh, just to prevent a few vehicles getting to Edinburgh Castle car park, is inefficient, wasteful and bound to have knock-on effects on lots of other routes.

Neil McIntosh uses the Edinburgh Castle car park as an analogy to explain the effects of the chemicals used to treat arthritis in dogs.Neil McIntosh uses the Edinburgh Castle car park as an analogy to explain the effects of the chemicals used to treat arthritis in dogs. (Image: Google Street View) So there are some drugs that don’t do that. In particular, there is one that quite specifically prevents the production of the most important prostaglandin that causes pain, inflammation and the deterioration of joints.

In my analogy, it stands at the entrance to the Edinburgh Castle car park, and proudly and resolutely defends it against entry. Happily, this reduces the painful clinical signs we see in arthritic dogs, without causing any of the numerous upsets associated with other medications.

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We have seen good results with it in patients who experienced side-effects with other drugs, but it is important to carefully discuss any proposed changes to medication care with your vet, especially if your pet is currently comfortable. Of course, the drug will not suit everyone, but for others it can be a life-changer.

(With apologies to the good people of Edinburgh.)

(No vehicles were injured during the course of this article.)