Arthritis

Brenda G. Mills, DVM
Arthritis is a condition affecting the joints.  It can affect any moving joint in the body, including the joints of the
legs, paws, spine and jaw.  Arthritis occurs when the shape of the joint is imperfect, either because of a genetic
conformation defect (i.e. hip dysplasia), injury to the joint or to the structures stabilizing a joint (a fracture or a
ligament injury), or normal wear and tear (old age).  Imperfections in the surfaces of a joint increase friction, and
arthritis is the joints’ way of attempting to increase stability.

Parts of a Joint:

All joints where movement occurs contain the following structures:

Articular surface:  This is the bony surface involved in the joint, where movement occurs.  There are two or more of
these in each moveable joint.

Cartilage:  A cushiony, resilient, rubbery tissue that covers articular surfaces.  Cartilage decreases friction and
absorbs and distributes the shock of impact in the joint.

Joint fluid:  A thick fluid which, similar to oil in a car engine, lubricates the joint.  The fluid also helps distribute and
absorb the shock of impact.

Joint capsule:  A fibrous tissue that surrounds the joint.  The capsule keeps the joint fluid within the joint space.  
Special cells in the joint capsule are responsible for producing and maintaining the joint fluid.

Tendons:  Tendons attach muscle to bone, permitting muscle to act on a joint to create movement.

Ligaments:  Ligaments attach bone to bone.  They are tough, fibrous bands that help hold the bones of a joint together,
keep joints stable, and help keep them from bending “in the wrong direction.”

Friction and Inflammation

Damage to any of these components will affect the overall structure of a joint by creating friction or instability.  The
bones involved in a joint will modify in response to instability in an attempt to restore normal function.   
Unfortunately, bone is not a very intelligent tissue, and these structural changes usually create more friction within

the joint rather than less.  The increased friction wears thin spots or holes in the cartilage, causing the bone to
attempt to adapt further, resulting in more friction. Inflammation then follows, which causes the joint fluid to
become thinner, making it a less effective lubricant, increasing friction and causing the joint to be painful.  Treating
arthritis, then, focuses on decreasing inflammation, usually with non-steroidal anti-inflammatory drugs (NSAIDs),

and preserving or improving joint fluid quality (often with glucosamine, chondroitin, or other nutritional supplements).


Non-Steroidal Anti-Inflammatory Drugs (NSAIDs)

NSAIDs are drugs that inhibit inflammation by affecting the function of an enzyme in the “inflammatory cascade” (a
series of chemical reactions that results in inflammation).  There are two forms of the enzyme that NSAIDs can
interfere with, cyclooxygenase 1 and cyclooxygenase 2 (COX1 and COX2).  COX1 is present in many tissues and
participates in normal function, while COX2 is almost exclusively involved in inflammation.  Certain NSAIDs affect
one form of the enzyme more than the other.  It is preferable to use NSAIDs that are COX2 specific because they are
less likely to cause side effects like stomach ulcers than drugs that affect COX1.  NSAIDs that are COX2 specific in
one species may be less COX2 specific in others, meaning that drugs that appear to be highly effective in humans

may be less effective in dogs, and vice versa.  






















Aspirin

Aspirin is the NSAID most commonly used by the general public.   Aspirin is not COX2 specific, meaning that there
is a significant potential for the development of adverse reactions such as gastrointestinal ulceration.   The
effectiveness of aspirin varies greatly based on the preparation and manufacturer.  The dose that is generally required
for control of arthritic pain in dogs was shown to cause stomach or intestinal ulcers in 50% of the dogs in one study.  
We do not recommend aspirin for the pain control on a day to day basis.  

Rimadyl (Carprofen)

Carprofen was the first prescription NSAID approved for use in dogs in the United States.  Carprofen is more potent
than aspirin, and appears to be relatively COX2 specific.  Carprofen has a very low incidence of causing intestinal or
stomach ulcers.  There is a low risk (0.02%) of developing liver disease while on Carprofen, and a lower risk of
injury to the kidneys.  In almost all cases, stopping the drug and administering supportive care leads to complete
recovery.  

We prescribe carprofen for arthritic pain and for pain associated with trauma.  Carprofen is given twice daily.

EtoGesic (Etodolac)

Etodolac appears to be relatively non-COX-specific in the dog.  It has a higher risk of causing ulcers, but a lower
risk of liver or kidney problems than Carprofen.  The risk of developing stomach or intestinal ulcers appears to be
dose-dependent, meaning that the risk is increased with higher doses (i.e. greater than the prescribed dose).  

EtoGesic is given once daily.  We prescribe it for long-term control of arthritic pain or for pain associated with

injury or trauma.  In some patients, EtoGesic appears to work better than Rimadyl.

Deramaxx (Deracoxib)

Deracoxib is a coxib class NSAID, similar to Celebrex.  The coxibs almost exclusively affect the COX2 enzymes,
significantly reducing the incidence of adverse effects and increasing the effectiveness of the drug.  At high doses,
Deramaxx may cause kidney parameters to become elevated, but safety studies showed no adverse effects on
monitoring blood work performed on dogs given the label dose.  Deramaxx is has been associated with severe
adverse reactions and even death when given long-term at doses greater than the label dose or when given in
conjunction with steroids or other NSAIDs.

Deramaxx is given once daily and is used for chronic arthritic pain as well as for post-operative pain at a higher
(short-term) dose.  Deramaxx has shown to be significantly more effective for pain control than Rimadyl in many dogs.

Metacam (Meloxicam)

Metacam is an oxicam-class NSAID which has been used successfully in humans.  Metacam was approved for use in
dogs in Europe several years before receiving approval in the United States, and is approved for use in cats.  
Metacam is delivered as a liquid which most dogs seem to find palatable, dosed at “one drop” per pound of body
weight or per a specially labeled syringe.  Metacam has proven to have a very low incidence of gastrointestinal
effects, but is known to cause kidney failure with chronic overdosing.

Metacam is given once daily to dogs for chronic arthritic pain and sometimes for post-operative pain after giving a
dose of the injectable product first.  Metacam is given once every three days to cats for the control of post-operative
pain or for chronic arthritic pain.

Previcox (Firocoxib)

Previcox is the newest of the coxib-class NSAIDs to be approved for use in dogs.  It is the first NSAID ever to be
developed specifically for dogs – previously, all NSAIDs approved for dogs have been drugs that have been
developed for human use (and in some cases failed the protocols for human use).  Based upon the safety tests,
Previcox appears to be the NSAID least likely to cause gastrointestinal ulceration or adverse reactions in any organ.  
Previcox is also the only NSAID to have been tested in puppies, which experience the greatest risk of adverse
reactions with any NSAID.  In clinical trials, Previcox compared favorably to Rimadyl and Etogesic for pain control,
and Previcox has in our experience proven to provide pain control superior to that of any other NSAID.

Previcox is given as a once daily chewable tablet for the control of pain due to acute injury, chronic inflammation, or
post-operatively.

Phenylbutazone

Phenylbutazone (“Bute”) was one of the earliest prescription NSAIDs available for veterinary use.  Phenylbutazone
causes bleeding disorders, liver disease, and kidney problems at a much higher rate than newer prescription NSAIDs.  
Phenylbutazone has also been shown to cause cartilage to break down.  We do not recommend phenylbutazone for use
in small animals.


Over-the-counter NSAIDs should be used with extreme caution in pets.  Naproxen (Anaprox) and Ibuprofen
(Advil, Midol) cause severe intestinal ulcers at low does in dogs.  Acetaminophen (Tylenol) can cause severe illness
at high doses.  Please call our office to check safety and dosages prior to giving your pet any over-the-counter drug.  
These drugs are not recommended for long-term use.

Chondroprotective Drugs

“Chondroprotective” is the term used to describe any drug acting to inhibit damage to or promote the regeneration of
cartilage.   These drugs are useful in the long-term treatment of arthritis, slowing the progression of arthritis,
decreasing pain, and frequently decrease the need for NSAIDs.  Chondroprotective drugs are also beneficial in
athletic and long-backed animals, helping reduce the risk of developing arthritis due to day-to-day trauma.  We
currently recommend the use of chondroprotective supplements such as glucosamine in all pets, regardless of their
age, as a preventive measure.

Adequan

Adequan is an injectable drug which has been shown to inhibit the degradation of cartilage by improving the
viscosity of joint fluid (making the fluid thicker), mimicking the glycosaminoglycan that occurs naturally in joint
fluid.  Adequan also promotes cartilage repair, though how it does this is not known.  The only adverse effects seen
with Adequan use is prolonged bleeding times (at high doses) and occasional pain and swelling at the site of
injection.  Adequan is given twice weekly for four weeks, followed by oral chondroprotective drugs.

Glucosamine

Glucosamine is a precursor to the molecule in joint fluid that Adequan mimics.  Studies in humans and animals have
indicated a significant improvement in mobility, decrease in pain, and inhibition of the progression of arthritis with
the use of glucosamine.  Glucosamine use can significantly decrease the need for NSAIDs.  Glucosamine is

available in both human and veterinary formulations.  There is a difference between glucosamines.  Glucosamine
HCl is the best absorbed, followed by glucosamine sulfate.  Other chemical forms of the molecule are so poorly
absorbed as to be virtually useless.  Consumerlabs.com tested 20 different glucosamine products sold for human use,
and found that only one brand, Cosamin by Nutramax Labs, actually contained the amount and form of glucosamine
stated on the label.  Purchasing a less expensive formulation of glucosamine will not necessarily be cost effective.  
Ask your veterinarian about the preferred products at this time.

Chondroitin

Chondroitin is an important part of the fibrous component of cartilage and also inhibits the activity of enzymes that
degrade joint fluid.  The concentration of chondroitin in joint fluid decreases with age, which may contribute to the
formation of arthritis in older animals that had good joint conformation as youngsters. Chondroitin in a purified form
is well-absorbed; chondroitin present in shark cartilage and other “natural” preparations is less readily available to
the body.  Chondroitin is available as a human preparation or in veterinary supplements.  Many of these supplements
contain glucosamine as well.  Chondroitin with glucosamine is generally regarded as more effective than either alone.

Superoxide Dismutase (SOD)

Superoxide Dismutase is an enzyme that occurs naturally in many tissues.  This enzyme acts as a “free radical
scavenger” (antioxidant) – it binds byproducts of inflammation that may be toxic to tissues.  Superoxide dismutase
may help reduce the need for other anti-inflammatory medication, and has a very wide margin of safety with very low
risk.

Antioxidant vitamins (A, C, E)

The antioxidant vitamins act as free radical scavengers, similar to superoxide dismutase.  While their action is less
potent and less specific than that of superoxide dismutase, they may help mitigate damage secondary to chronic
inflammation.  Care should be taken, though – studies have shown that giving dogs high doses of vitamin C and then
withdrawing the vitamin suddenly may cause symptoms of scurvy.

Chiropractic care

Chiropractic care may not inhibit the progression of existing arthritis, but can help optimize the function of arthritic
joints.  Chiropractic adjustments can also help your pet compensate for achy joints by assisting the body in correcting
trauma caused to other joints by the abnormal stresses created when an animal shifts weight off of a sore limb.  
Chiropractic adjustments can also help delay the onset of arthritis due to chronic injury by restoring joint motion after
injury and assisting the body in healing mild joint trauma.  

Acupuncture

Acupuncture is an ancient method of disease treatment dating back at least 2000 years.  The insertion of needles into
acupuncture points is believed to stimulate nerves, modifying the conduction of sensory input such as pain and
possibly initiating a feedback loop that can result in the reduction of inflammation.  Acupuncture is currently
recommended by many pain control specialists working in human medicine.

THE BOTTOM LINE

Arthritis is an age-associated disease, and is responsible for most of the “slowing down” that we recognize in older
pets.  The severity of the pain associated with the arthritic changes is very dependent upon the individual – our
tolerance to pain, obesity, how gradually the pain sets in, the joints affected, and our ability to compensate.  
Depending upon the stage of the arthritic changes, multiple treatment modalities are available, ranging from dietary
supplements and chiropractic care to NSAIDs and opiods or acupuncture.

To borrow a quote from the Deramaxx ad campaign, “No (pet) should be in pain.”

We recommend that all arthritic patients receive physical examinations once every six months, to monitor overall
health status and the progression of arthritis.  Little things like being 10% overweight can have a dramatic negative
impact upon the ability of an arthritic pet to get through the day.  For patients on long-term medication, especially
NSAIDs, some degree of laboratory monitoring is recommended every six months as well.  Even in the absence of
long-term medication, blood work is advisable to monitor thyroid level, urinary health, and other factors that can
adversely affect your pet’s well-being.
We do recommend running screening blood work prior to giving any NSAID long term, and every 6 months while
the patient is on the drug.  Even the safest, most COX2-specific NSAID must be used with caution in animals with
kidney, liver, or other metabolic diseases.  Toxicity may occur in sick patients which would not occur in
metabolically normal animals.  The goal of performing monitoring blood work is to prevent such toxicities by
catching any abnormality while it is still a laboratory value and before it becomes a problem for the patient.
A
serious, potentially life-threatening adverse reaction can happen with the use of any NSAID, even Tylenol in people.
Vomiting, diarrhea, intestinal or stomach ulcers, and circulatory problems are the most common adverse reactions.
If your dog seems to be ill in any way while taking an NSAID, stop giving the drug immediately and call us for an
appointment.  We will do a physical exam and check blood work to rule out liver or kidney problems.
Giving two different NSAIDs together can result in rapid onset, severe adverse reactions, including death.  If your
pet is on an NSAID, please remember that it may be extremely dangerous to give your pet anything additional for
pain or to increase the dosage of the NSAID you are using.  If your pet’s pain becomes too severe to be adequately
controlled by the dose of the NSAID you are using, please contact your veterinarian about switching drugs or

adding an opiod such as tramadol or codeine.  When switching NSAIDs, a “drying off” period is typically
recommended to make certain that the previous drug is completely out of the animal’s system prior to starting the

new drug, minimizing the potential for adverse reactions.  Two weeks is generally accepted as “safe,” but in many
cases it is unacceptable to leave the pet without NSAIDs for two full weeks, and a one week or shorter period
without drugs may be recommended prior to starting the new drug.  Steroids should be avoided or used with extreme
caution in animals that are taking any NSAID.
This client information is written by Dr. Brenda Mills, DVM
Copyright 2002