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.

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 flavors.

Nonpharmacologic intervention

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.