Are long term painkillers safe for my horse?

Most horse owners will have experience of administering NSAID or antiinflammatory drugs to their horse at some point. It is rare to find a horse that has not needed pain relief for any number of conditions such as injury colic or laminitis to name just a few! However it can be easy to become complacent about their use given how commonly they are prescribed. In this article we ask what these drugs are and if they are as safe as we would like them to be. 
What are Nonsteroidal antiinflammatory drugs NSAIDs?
These drugs belong to a group used to provide pain relief reduce swelling and inflammation. In terms of pain they act to block inflammatory pathways bringing relief from pain. They also have the ability to treat endotoxaemia. Endotoxaemia is a condition that may arise as a result of colic or sepsis such as retained placenta amongst other conditions. The earliest commercially produced NSAID was aspirin. Interestingly the active agent in this drug is salicin which is found in the bark of the willow tree used by humans 3500 years ago for the relief of fevers or pain! 
These drugs act on a group of receptors known as COX. The COX enzymes are responsible for pain fever and inflammation and the NSAIDs act to reduce this response. They are called nonsteroidals to distinguish them from steroids which can also reduce inflammation but act in a different way. 
The most commonly used NSAID for horses in the UK is phenylbutazone often known as Bute
This is usually administered intravenously by a veterinary surgeon or orally as a paste or powder by owners or carers. Like all licenced NSAIDs it can only be prescribed by a veterinary surgeon. It is also worth noting that before prescribing or using phenylbutazone the veterinary surgeon must check your horses passport to ensure that it has been signed to declare that the horse will never enter the human food chain. We have NSAIDs that are licenced for food producing animals. But they can be more expensive in some cases but offer a good alternative if your passport is not available or in certain conditions. 
Are NSAIDs safe?
Administration of an NSAID like most drugs can result in toxicity. It has been established that phenylbutazone is one of the more likely NSAIDs to induce toxicity in the horse. The risk of toxicity is dependent on a number of different