As with dogs, monitor cats receiving NSAIDs for chronic pain for side effects related to renal and hepatic function and gastrointestinal
erosions. No monitoring guidelines have been established, but a serum chemistry profile, packed cell volume, and total protein
measurement are recommended before you initiate treatment and should be repeated at one and four weeks. After this, the timing
of follow-up blood work is arbitrary and will vary in each patient. As with dogs, it is important to discuss the possible
side effects of these drugs with the owner, and if vomiting or anorexia occurs, the client should stop administration and
seek veterinary advice. It is also imperative to inform the owner that under no circumstances should any over-the-counter
anti-inflammatory drugs such as aspirin be given in conjunction with an NSAID. Continual reassessment of the patient both
by the veterinarian and owner is important so that the dose can be tapered to the smallest effective amount.
Opioids. In my experience, because of their side effects such as euphoria, inappetence, and constipation after long-term use (days
or weeks), opioids are best reserved for terminal or hospice care in cats or for occasional breakthrough pain while the cat
is receiving other analgesics or undergoing other treatment modalities.
Other analgesic drugs. The role of other drugs in alleviating chronic osteoarthritis-related pain has not been well-studied in cats. Several drugs
have, however, been suggested.
Tricyclic antidepressants including amitriptyline, clomipramine, and imipramine can provide relief in people with chronic
neuropathic pain and are thought to alter the actions of serotonin and norepinephrine both centrally and peripherally.13 Anecdotal reports suggest that amitriptyline (between 2.5 and 12.5 mg for an adult cat orally once a day) may be effective
for chronic pain syndromes in cats including osteoarthritis.
The anticonvulsant gabapentin is clinically effective in relieving some types of chronic pain in people, although the mechanism
of action is not clear.14 Individual case reports demonstrate that gabapentin shows promise in cats,15 and doses starting at 10 mg/kg given orally twice a day have been suggested.16 Some animals become sedate and occasionally ataxic when given gabapentin. These signs may decrease as a cat acclimates to
the drug or can be managed by decreasing the dose. In my experience, the tablet and capsule formulations of gabapentin are
more palatable and easier to administer to cats than the liquid oral formulation, and they don't contain xylitol.
Although not classified as an opioid, tramadol has weak binding affinity at mu-receptors. It is thought to activate monoaminergic
spinal inhibition of pain, although this may not apply to nonprimate species. It can be administered by multiple routes, including
orally, is effective for relieving moderately severe acute and chronic pain in people, and seems remarkably devoid of the
usual undesirable side effects of opioids such as respiratory depression and tolerance.17 The pharmacokinetics of tramadol and its major metabolite has recently been reported in cats18 ; doses in cats would likely be less than those in dogs (on a mg/kg basis) and the dosing interval may be longer. As of yet,
no published studies have reported tramadol's efficacy for relieving osteoarthritis pain in cats. The chief problem with tramadol
is its bitter and unpleasant taste, which makes administering it to cats difficult, even after compounding with fish or chicken
Rehabilitation therapy (underwater treadmill, passive range of motion, creative exercise techniques), nutraceuticals (e.g. chondroitin sulfate), and acupuncture are also used to treat osteoarthritis in cats with varying success. Many cats are
more tolerant of these interventions than you might think.
Editors' note: Dr. Robertson has received financial support from Boehringer-Ingelheim Vetmedica to conduct workshops for Boehringer-Ingelheim
veterinarians, write one review article, and speak at veterinary continuing education meetings.