NSAIDs - Research Article
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| Definition | Types of NSAIDs | Side Effects / Dangers |
| Safety Concerns |
Definition / Overview
The number one cause of chronic pain in dogs and cats is degenerative joint disease, the two most common forms of which are arthritis and hip dysplasia.
Arthritis is a general term for abnormal changes in a joint. Arthritis can arise from joint tissue destruction subsequent to an infection, from congenital defects affecting structural architecture, and from stress and trauma to joint surfaces and supporting structures. Occasionally, disorders of the immune system lead to joint tissue inflammation and degeneration.
Hip dysplasia is an abnormal function of the hip joint, which occurs when the fit between the ball and socket of the hip joint loosens. Most of the problems resulting from hip dysplasia are a result of this looseness, the loss of tension in the muscles, connective tissue, and ligaments that should support the joint.
The most common group of drugs recommended by veterinarians for the treatment of arthritis and hip dysplasia, NSAIDs (nonsteroidal anti-inflammatory drugs) have been used to treat joint disorders in pets since 1989, and they have gained in popularity as the risks of prolonged steroid use have become apparent in recent years. These non-addictive drugs have analgesic (pain relieving) yet non-narcotic (non-numbing), antipyretic (fever reducing), and anti-inflammatory effects.
How NSAIDs Work
NSAIDs control the pain and inflammation associated with osteoarthritis and hip dysplasia. They work by blocking the production of prostaglandins, the chemicals that cause inflammation, in the COX pathway. COX stands for cyclooxygenase, which is another enzyme in the pathway that breaks down the arachidonic acid in the cell membranes of the joint into chemicals such as free radicals and various prostaglandins that damage the articular cartilage.
To date, two COX enzymes have been discovered: COX-1 and COX-2. COX-1 is found in various tissues, including those of the stomach, intestines, and kidneys, and serves an important role in maintaining health. When arachidonic acid is broken down by COX-1, anti-inflammatory prostaglandins are produced. These prostaglandins keep the kidneys functioning normally and help protect the stomach and intestinal tract against ulcers.
Drugs that selectively inhibit COX-2 but not COX-1 are most likely to result in fewer side effects and to be safer for patients. Right now, the move is on in human medicine to find NSAIDS that inhibit COX-2 but not COX-1. Our veterinary patients will benefit from this research as well.
Current NSAIDs available for veterinary patients inhibit both COX-1 and COX-2, to varying degrees. Piroxicam, for instance, has a high COX-2/COX-1 ratio, and results in high incidences of gastrointestinal problems, such as bleeding and ulcers. Naproxen, carprofen, and etodolac have lower COX-2/COX-1 ratios, and as a result have fewer incidences of gastrointestinal problems. Aspirin has a higher ratio, but an intermediate incidence of gastrointestinal problems, indicating that other mechanisms are involved in causing some of the side effects we may see in patients taking NSAIDs.
Because of the unique biochemistry and liver function of cats, NSAIDs are even more dangerous to them. None of these drugs have been approved for use in cats, though some veterinarians will prescribe them for cats, as alternatives are not available and pet owners are desperate to provide relief to their cats.
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