Inflammation and prostaglandins
Inflammation is a normal reaction to protect the body from harmful pathogens or irritants and to promote healing of damaged tissues. It is complex process of cellular interactions of the immune system that is mediated by certain chemicals produced at the site of tissue damage, infection or trauma. Symptoms of inflammation include redness, heat, swelling and pain or discomfort.
The process of inflammation includes the widening and increased permeability of small blood vessels, exudation of fluid and migration of immune cells like macrophages and neutrophils into the tissues where damage, infection or irritation has occurred. The fluid causes swelling and the cells produce inflammatory chemicals like prostaglandins, interleukins and leukotrienes. These chemicals attract more inflammatory cells to help with wound healing and disposing of harmful pathogens but they also magnify the inflammatory response. In doing their job, some of these inflammatory mediators can also cause pain, swelling, fever and redness. If the inflammatory process continues beyond protecting and healing it becomes chronic and can end up damaging normal tissues.
Nonsteroidal anti-inflammatory drugs (NSAID)
Nonsteroidal anti-inflammatory drugs (NSAID) are medications that inhibit cyclooxygenase (COX), an enzyme involved in the synthesis of prostaglandins like PGE2, which have important functions throughout the body but are also potent inflammatory mediators and cause pain, swelling and other symptoms of inflammation. They are called nonsteroidal as corticosteroid drugs are also used to treat inflammation but target a different enzyme in the pathway of prostaglandin synthesis.
There are two main COX enzymes, COX-1 and COX-2. COX-1 is present in most cells and plays an important role in many normal cell functions, including aggregation of blood platelets, which controls bleeding; protection of the stomach lining or mucosa by promoting cell growth; also in maintaining normal kidney function by regulating blood flow. COX-2 is only produced by inflammatory cells, and is induced during the inflammatory process, although it is also found in very small amounts in some tissues.
Some NSAIDs like phenylbutazone and carprofen inhibit both COX-1 and COX-2, which is the cause of the more serious side effects of non-specific COX inhibitors. These include gastric bleeding and ulcers due to the inhibition of prostaglandins that are protective of the stomach lining and have vasodilator (cause widening of blood vessels) action which helps maintain normal blood flow. Kidney damage is also a potentially serious side effect and again this is due to the inhibition of protective prostaglandin production by blocking COX-1. Meloxicam and firocoxib are specific COX-2 inhibitors and have no inhibitory action against COX-1, which makes them more effective for pain and inflammation, without the gastrointestinal or kidney side effects associated with COX-1 inhibition.
Inflammation and pain occur due to several chronic and acute conditions in animals, including:
- Inflammatory joint diseases like osteoarthritis, a degenerative disease of the joints caused by wear and tear where the cartilage around the bone is worn away. It is a common condition in many dogs, particularly as they age, which restricts mobility and can cause lameness.
- Soft tissue injuries, such as sprains and strains that are due to trauma to the tendons, ligaments, muscles or joints.
- Following orthopaedic and soft tissue surgery.
Anti-inflammatory medications for veterinary use
These anti-inflammatory medications are generally specifically indicated for veterinary use.
- Phenylbutazone is an oral paste used to treat pain and inflammation in horses caused by joint and soft tissue injury
- Carprofen is a non-specific oral anti-inflammatory used to treat dogs to help manage the pain and inflammation caused by osteoarthritis.
- Meloxicam oral suspension and firocoxib chewable tablets are specific COX-2 inhibitors used to relieve pain and inflammation due to osteoarthritis in dogs and following orthopaedic and soft tissue surgery.