Drug treatments for osteoarthritis have one of two primary objectives: Firstly, to make the patient more comfortable i.e. reduce the symptoms and signs of the condition. Secondly, and this is one of the major goals of osteoarthritis research, to slow or even reverse the osteoarthritis process that is causing progressive deterioration and loss of articular cartilage. Compounds that can slow the osteoarthritis process down are referred to as Disease (or structure) Modifying Drugs (DMOADs).
In clinical practice for both humans and dogs, the concept of disease modification is still rather theoretical with no treatment proven to have this effect. The main second line treatments in small animal veterinary practice are anti-inflammatory drugs.
Most canine patients with some lameness associated with osteoarthritis will be best treated with anti-inflammatory drugs.When we talk about anti-inflammatories and OSTEOarthritis we are virtually always referring to the Nonsteroidal anti-inflammatories or the NSAIDs (pronounced as ‘en-sayds’).
The NSAIDs are a group of quite different drugs but they all work in a similar way. They all act to block the production of prostaglandins in body tissues. Prostaglandins are a family of chemicals produced by the body that promote inflammation, pain, and fever. As well as making the local blood capillaries more leaky (causing local swelling) they will make nerve fibres more sensitive and hence make us feel pain.
Anti-inflammatory drugs act to reduce prostaglandin production in the tissues and hence reduce inflammation and discomfort. Prostaglandins also have some beneficial and important protective effects in the body. These include regulating blood flow to the kidneys and maintaining a protective mucus barrier in the lining of the stomach. It is in blocking these actions as well as the ‘bad’ effects of prostaglandins that NSAIDs can cause some nasty and potentially fatal side effects.
NSAIDs act by blocking the action of an enzyme called cyclooxygenase (COX), which is vital to the production of prostaglandins in the tissues. There are at least two forms of this enzyme referred to as COX-1 and COX-2. Nonsteroidal anti-inflammatory drugs (NSAIDs) block the COX enzymes and reduce prostaglandins throughout the body. As a consequence, ongoing inflammation, pain, and fever are reduced.
Since the prostaglandins protect the stomach and maintain a healthy blood flow to the kidneys, NSAIDs can cause stomach inflammation, gastrointestinal ulcers and cause kidney damage by reducing renal blood flow. The risk of serious kidney damage is magnified in dehydrated patients or patients in circulatory shock from blood loss. COX-1 is particularly important in housekeeping functions and COX-2 is increased in the presence of inflammation. NSAIDs that preferentially block COX-2 seem to cause fewer gastrointestinal side effects.
COX-2 selective NSAIDs have become available for use in the dog. Three of the newer and most widely used agents, Metacam, Rimadyl and Previcox are licensed for use in a number of countries. They show preferential inhibition of COX-2 and show a lower incidence of side effects compared to drugs such as aspirin.
Generally anti-inflammatories alone seem to work well in the dog with arthritis. There are some drawbacks, mainly vomiting and diarrhoea, which can limit their usefulness in some patients and, lead to very serious complications in some. Their effects on reducing blood flow to the kidneys can be devastating in certain situations, typically those where there is some form of circulatory system problem such as shock or dehydration.
Play it Safe
Although NSAIDs have been associated with some serious side effects and adverse reactions, they provide safe, effective pain relief in the vast majority of patients. However, they are potentially very dangerous drugs and should be respected. I would advise the following rules are adhered to in order to minimize the chances of adverse reactions:
1. Only use a veterinary licensed product provided/recommended by your veterinarian. Some human preparations have a much narrower safety profile in dogs than in people. Don’t do it!
2. Stop using any NSAID immediately if your dog develops inappetance, vomiting and or diarrhoea. Consult your veterinary professional straightaway.
3. Always consult your veterinarian before administering any other medications alongside NSAIDs.
4. If at a veterinary visit you see a different person at the clinic, always remind them that your dog is on NSAIDs – It should be on your pet’s clinical notes but better to play it safe and mention it.
The NSAIDs are an important component of your pet’s arthritis treatment plan but they should be used with care and under the strict guidance of your vet. They are just one factor in successfully managing canine osteoarthritis.