Answering Your Questions: Practical analgesia in cats
Q What criteria do you use to determine the need for analgesia in cats?
Because cats are relatively quiet creatures, that is, they don't bark, whine, and announce themselves, their analgesic needs are often ignored or forgotten. Evaluating pain in cats is challenging and requires intense and prolonged observation, intuition, interaction with the animal, and knowledge of the various feline behaviors that may signal pain. Sometimes the owner can best evaluate a cat's pain, as he or she knows the animal's normal behavior better than anyone else. Cats have evolved to hide their pain, so their behaviors associated with pain may be subtle.
Behaviors that may signal pain in cats include lack of grooming; sleeping a lot; lack of interest in food, water, or their environment; sleeping in only one position; wanting to be left alone; growling or hissing when stroked, touched, palpated, or moved; relentless purring; abnormal body postures such as a hunched-back, head-in-the-corner stance; and restlessness. Cats may also change their preferred sleeping places, food preferences, or litter box habits. This is only a partial list of behaviors cats might exhibit when analgesics are needed.I like to use analgesics as a tool to evaluate a cat's pain, especially when the presence of pain is not clear-cut. Of course, if a cat has recently undergone surgery that is expected to be painful, such as an orthopedic procedure, I never withhold analgesics, even if the cat's behavior seems normal. But if a cat has vague clinical signs or several days have elapsed since a painful surgery, I administer an analgesic and observe the resulting behavior as a way to assess whether pain was a component of the clinical presentation.
For example, a cat with gingivitis and periodontal disease may be inappetent, dehydrated, depressed, or just "not doing right," but it may not demonstrate clear signs of pain. A short course of low-dose opioid analgesia (e.g. buprenorphine hydrochloride for at-home oral transmucosal administration or a preplaced fentanyl patch) may improve the cat's attitude and appetite. This results in a normally hydrated cat that feels better and is now a better candidate for general anesthesia and its dental procedure.
Q What opioids are best for cats? Are morphine side effects dose-dependent?
The choice of the most appropriate opioid for cats depends on personal preference, the degree of analgesia required, the desired duration of effect, the practical routes of administration under the circumstances, and the availability of the drug. All of the agonist opioids available in the United States (e.g. morphine sulfate, oxymorphone hydrochloride, hydromorphone hydrochloride, and fentanyl) are good analgesics for moderate to severe pain when given at appropriate doses. Buprenorphine, a partial agonist, is appropriate for moderate pain in cats, and some studies suggest it provides analgesia superior to oxymorphone, morphine, and meperidine hydrochloride.1-3 Buprenorphine is well-absorbed when given by the oral transmucosal route,4 making it easy to prescribe for at-home use. I do not find injectable butorphanol tartrate, a mixed agonist-antagonist opioid, useful for severe pain in cats, but it is beneficial when minor pain relief is needed for a short duration (i.e. one or two hours). Oral butorphanol is not well-absorbed and likely provides little to no analgesia.