QPlease provide educational material about canine chronic pain management for the client that is not commercially prepared.
AAt the recent Southwest Veterinary Symposium of 2003 in Fort Worth, Texas, Dr. Darryl L. Millis from University of Tennessee
presented an excellent talk on chronic pain management that would be appropriate for the client and is not commercially based.
Selected aspects from his presentation follow.
Chronic pain is frequently associated with orthopedic conditions, such as osteoarthritis. Other conditions resulting in chronic
pain include neoplasia, neurologic conditions, myopathies and chronic inflammatory conditions.
Animals with chronic painful conditions generally do not display many of the dramatic painful behaviors associated with acute
pain. For example, dogs with osteoarthritis may have restricted activity, limited ability to perform, muscle atrophy, pain
and discomfort, decreased range of motion and decreased quality of life. Other signs of chronic pain include reduced appetite,
licking the area and laying quietly in an area free of other activity.
As animals reduce their activity level because of chronic pain, a vicious cycle of decreased flexibility, joint stiffness,
loss of strength and decreased cardiovascular fitness occurs.
Management of dogs with chronic pain should include medication and physical modalities. Medication for chronic painful conditions
should reduce pain and discomfort, decrease the severity of clinical signs, maintain an acceptable quality of life, improve
strength and fitness, slow the progression of the underlying disease if possible and promote the repair of damaged tissue.
Surgical treatment may focus on correcting the underlying condition, or performing a salvage procedure such as a total hip
replacement for hip dysplasia or amputation for osteosarcoma.
Managing painManagement of dogs with chronic pain due to osteoarthritis includes anti-inflammatory and analgesic medications, disease-modifying
osteoarthritis agents, weight reduction, low-impact exercise programs and physical modalities, alteration of the environment.
The management of chronic osteoarthritis is a lifelong commitment and requires diligent effort and regular follow-up assessments.
Many inflammatory mediators may be involved in chronic painful conditions, including prostaglandins, leukotrienes, interleukins
and metalloproteinases. It is possible that nonsteroidal anti-inflammatory agents (NSAIDs) provide benefits to arthritic dogs
in several ways. One of the primary modes of action is the reduction of inflammatory mediators, especially prostaglandins,
in the peripheral tissues and in the central nervous system. The inflammatory cascade is initiated when cell membrane phospholipids
are acted on by phospholipase to produce arachidonic acid. Cyclooxygenase (COX) and lipoxygenase then act on arachidonic acid
to produce eicosanoids, such as prostaglandins and leukotrienes.
NSAIDs inhibit the COX enzyme, thereby decreasing the production of inflammatory mediators and reducing pain associated with
osteoarthritis. Recently, two forms of the COX enzyme have been identified, COX-1 and COX-2. COX-1 is a constitutive enzyme
and is normally produced in relatively constant amounts and has "house-keeping" functions, such as protection of the gastric
mucosa, maintaining renal perfusion and production of platelet thromboxane A2. The COX-2 enzyme is inducible and its production
increases in response to inflammation.
In addition to the induction of COX-2 in peripheral tissues with inflammation, COX-2 is also induced in the central nervous
system. The inhibition of the COX-1 enzyme by NSAIDs is believed to be responsible for adverse side effects, including gastric
ulceration, platelet dysfunction and decreased renal perfusion.
Non-selective COX inhibitors inhibit both COX-1 and COX-2 enzymes. The identification of the two COX isoforms has resulted
in the development of products that preferentially or selectively inhibit the inducible "bad" COX-2 enzyme while sparing the
COX-1 enzyme. Selective inhibition of COX-2 with preservation of COX-1 should reduce the adverse effects associated with the
GI tract, kidneys and platelets. The concept of COX-1:COX-2 ratios helps in the understanding of the relative ability to inhibit
the various forms of cyclooxygenase. A ratio >1 indicates that the drug inhibits more COX-1 activity than COX-2 activity,
while a ratio <1 indicates that the drug inhibits more COX-2 activity than COX-1 activity. Theoretically, fewer side effects
should occur with a COX-1:COX-2 ratio >1.
Unfortunately, there are no standard ways of measuring this ratio, and ratios may be significantly affected by the type of
in vitro or in vivo test system, the substrates used, and the incubation times and conditions of the test system.
The best guidelines are the clinical efficacy of a particular drug, while maintaining an acceptable level and degree of side
effects. NSAIDs that are frequently used include deracoxib, carprofen, etodolac, and aspirin. Phenylbutazone, meclofenamic
acid, meloxicam, and piroxicam have also been used, and ketoprofen is approved for use in other countries and has been used
in the USA. Acetaminophen with or without codeine is occasionally used in dogs but should not be used in cats.
Deracoxib is a COX-2 specific inhibitor, as defined by the World Health Organization, while carprofen, etodolac, and meloxicam
have some preferential selectivity to inhibit COX-2. While no NSAID has been shown to clearly be more efficacious than others
in the relief of chronic pain, some dogs apparently have a better response to some drugs as compared with others. Veterinarians
should not be reluctant to perform therapeutic trials to evaluate the efficacy of various NSAIDs in a particular animal to
determine which will provide the best clinical improvement without side effects. Two-week trials of various NSAIDs with adequate
animal evaluation should be performed to determine which medication provides the best response. Before prescribing any medication,
the animal's health status, especially liver and kidney function, should be assessed. It is important to educate owners regarding
potential side effects.
Slow-acting disease-modifying osteoarthritic agents are substances which are thought to alter the course of osteoarthritis
by improving the health of articular cartilage or synovial fluid. Nutraceuticals are nutritional supplements believed to have
a positive influence on cartilage health by providing precursors necessary for repair and maintenance. Glucosamine and chondroitin
sulfate are routinely combined as disease-modifying agents.