Any drug prescribed to treat chronic pain must be in a formulation that is simple to administer and well-accepted by cats
to ensure optimal owner compliance.
NSAIDs. The mainstay of drug therapy for osteoarthritis in most species is an NSAID. These drugs pose a challenge in cats because
of cats' susceptibility to NSAID toxicosis, especially with long-term dosing. Pharmacokinetic data are only readily available
for single doses of NSAIDs in cats.* Most NSAIDs have a relatively long half-life in cats, and repeated dosing must be administered
and monitored carefully to avoid toxicosis. For example, gastrointestinal toxicosis has been reported with carprofen,8 and based on clinical experience, toxicosis is generally associated with concurrent disease and prolonged administration
of the oral formulation.Problems with repeated dosing are likely a result of individual variation in pharmacokinetics because
the half-life of carprofen in cats can vary from nine to more than 40 hours.9,10
One NSAID sometimes used to treat the pain and inflammation associated with osteoarthritis in cats is meloxicam, a COX-2 selective
NSAID available as an injectable and oral formulation. The injectable formulation is licensed in the United States for use
in cats to treat postoperative pain and inflammation but only as a single 0.3-mg/kg dose administered subcutaneously before
surgery. The honey-flavored oral liquid meloxicam marketed for dogs is widely used (extralabel) in cats in the United States
because it is palatable and small doses are easily measured. An oral formulation of meloxicam is now labeled for long-term
use in cats with musculoskeletal disease in many other countries; the registered dose is 0.05 mg/kg once daily.
One published study evaluated the use of short-term NSAIDs for musculoskeletal pain in cats. Sixty-nine cats with acute or
chronic locomotor disorders were randomly assigned to receive oral meloxicam or oral ketoprofen.11 Both drugs were equally effective based on general attitude, appetite, weight-bearing, lameness, and pain on manipulation,
but meloxicam was more palatable and easier to administer. In a prospective study of 28 cats, many cats with osteoarthritis
improved within one month with meloxicam intervention; 61% showed a marked improvement, 14% showed a moderate improvement,
and 25% showed a slight improvement.5
In a recently published study of 40 cats with osteoarthritis that were treated with meloxicam (0.01 to 0.03 mg/kg once daily
orally) for 5.8 ± 3.4 months,12 85% of owners scored the efficacy of meloxicam as good or excellent and thought that palatability was excellent. The 40
cats with osteoarthritis were paired with 40 control cats of similar age (12 or 13 years). No difference was noted in illness
events (type or number) between the two groups. No differences were found in serum creatinine concentrations between enrolled
and control cats before and after treatment. Three cats with preexisting renal disease were enrolled in the meloxicam group,
and the renal function of these cats did not deteriorate faster than that of the three cats in the control group that had
similar blood urea nitrogen and serum creatinine concentrations; however, no statistical analysis was possible because of
the small number of cats in this category.
With care, oral meloxicam can be used long-term in cats, and doses lower than those approved for use in cats in other countries
can markedly improve their comfort. Most owners are able to gradually decrease the dose to that which keeps their cats comfortable;
the key to successful long-term NSAID administration in cats is to use the lowest effective dose.
The most common side effect of orally administered meloxicam in cats is gastrointestinal upset. In one study, 18% of cats
showed intermittent signs of gastrointestinal upset (vomiting or diarrhea),5 but the signs were not severe enough to terminate treatment in any cat. In the largest clinical study to date,12 four out of 46 cats vomited during meloxicam treatment, and two of these cats were withdrawn from the study.
*For a comprehensive review of NSAIDs in cats see Lascelles BD, Court MH, Hardie EM, et al. Nonsteroidal anti-inflammatory
drugs in cats: a review. Vet Anaesth Analg 2007;34(4):228-250.