For painful perioperative conditions (e.g. orthopedic surgery), use the higher end of the dose range (i.e. 0.2 to 0.3 mg/kg subcutaneously one time), but use the lower end of the range (e.g. 0.1 mg/kg) for soft tissue pain or when initiating analgesic treatment for chronic pain. The one study examining use of meloxicam
in cats with chronic arthritic pain found that a once-daily dose given for no more than five days (0.3 mg/kg orally on Day
1, followed by 0.1 mg/kg orally on Days 2 through 5) provided significant improvement and no observed side effects.14 Renal function was not clinically assessed.14 These researchers found the same results with ketoprofen (1 mg/kg orally once daily for five days),14 but noted that meloxicam's palatability made it more attractive for long-term use.
Q Which NMDA-receptor antagonists can be used as analgesics in cats? What are the dosages and how effective are they?
An NMDA-receptor antagonist common in veterinary medicine is ketamine. There is a paucity of scientific literature regarding
ketamine's analgesic effect in veterinary patients. One study in dogs that received ketamine constant-rate infusion as adjunctive
analgesia to fentanyl constant-rate infusion found some benefit.23 Owners reported improved postoperative outcome in their dogs during the period immediately after an amputation compared with
dogs that received saline solution infusions as an adjunct to fentanyl.23 This benefit has not been scientifically established in cats.
Given that the NMDA receptor participates in the spinal cord dorsal horn wind-up that occurs with peripheral somatic, neural,
or visceral injury, it is probably valid to use ketamine in the perioperative period in cats to attenuate that wind-up. So
there is probably no harm in using ketamine in the anesthetic protocol as an adjunct to other analgesic agents. It can be
given intramuscularly as a premedication for its NMDA-receptor antagonistic effects. I have also used subanesthetic doses
of ketamine as a constant-rate infusion during surgery in cats to supplement my inhalant anesthetic and other injectable opioid
analgesics. I administer a 0.5 mg/kg intravenous bolus, followed by 2 to 10 µg/kg/min given intravenously. I cannot say with
assurance, however, that there is a clear analgesic benefit to this practice.
Q Which injectable or oral analgesics that can be used in cats have the longest duration of action?
Meloxicam and ketoprofen each have a duration of action of 24 hours after one oral dose but should not be given for more than
five consecutive days. As I discussed earlier, these should be administered cautiously.
Among the opioids, buprenorphine has the longest duration and has higher receptor affinity than other opioids, such as oxymorphone.
Buprenorphine has a dose range of 0.005 to 0.02 mg/kg and, at the higher doses, probably lasts about six hours after oral
transmucosal administration.4 This drug has a slow onset of action, taking about 45 minutes for peak effect after intramuscular or subcutaneous administration,
with somewhat faster absorption and onset of action after transmucosal administration.24 For effective and predictable analgesia, use the higher dose range transmucosally because it provides more reliable absorption
than the subcutaneous or intramuscular routes.4
Q What are the most common interactions to be aware of regarding analgesics and other drugs in cats?
Most drug interaction information is taken from research in people and extrapolated to veterinary patients. Because of species
differences in drug response, distribution, and metabolism, extrapolating from one species to another is not always an accurate
or appropriate approach. Cats in particular metabolize drugs differently than many other species since they do not synthesize
glucuronide metabolites. This means that drugs undergoing glucoronidation for metabolism will have prolonged effects in cats.