Update on feline anesthesia and pain management (Proceedings)
The emphasis on providing humane care and good pain management to small animal patients has primarily focused on dogs, and the pharmaceutical products available for use in that species. However, several analgesic and anesthetic products have recently been developed and approved by the FDA-CVM for use in cats. Given the increased public awareness, increased client expectations are impacting the care veterinarians are delivering to their feline patients. This lecture reviews some of the new products and clinical studies focused on feline pain management and anesthesia.
Pain Management for Cats
Practitioners should develop a comprehensive, individualized practice program for recognizing and managing pain. Many recent resources are available including journal articles and textbooks such as Lumb and Jones' Veterinary Anesthesia and Analgesia (1, 2). The management of pain in cats differs from that in the dog due to species differences in drug and technique effectiveness and toxicity of analgesic drugs including opioids and NSAIDs. Until recently, the only approved analgesic drug for cats was butorphanol. This lead to nearly universal extralabel drug use and increased practitioner liability. Some pharmaceutical manufacturers have responded to the need for approved feline products. Meloxicam (Metacam) and dexmedetomidine (Dexdomitor) have recently been approved for use as analgesics in cats.Dexmedetomidine
Dexmedetomidine (Dexdomitor) was approved in 2007 for use in cats as a sedative/analgesic. While medetomidine was used in cats previously, this usage was extra-label. Building upon practitioner experience with Domitor, Dexdomitor is now approved for use in cats (at a relatively low dose) to provide sedation and analgesia and to facilitate restraint for minor procedures. While analgesia accompanies sedation, practitioners should not rely on alpha 2 agonists alone in any species for surgical anesthesia. Local anesthetic blockade is recommended if surgical trauma is anticipated to prevent sudden arousal and defensive behavior from the cat.
Cardiovascular effects of alpha 2 agonists are similar to those reported in dogs. Animals that cannot tolerate a decrease in cardiac output, increase in vagal tone, or increase in systemic vascular resistance should not receive alpha 2 agonists. Dexdomitor can be antagonized by intramuscular administration of atipamezole (Antisedan). Intravenous administration should probably be reserved for emergency situations since antagonist induced rapid vasodilation in the presence of reduced sympathetic tone can lead to precipitous hypotension. While Dexdomitor is now an approved label use, atipamezole reversal in cats is not approved, although quite common.
Although meloxicam use in cats has been reported for several years, its use in the US was extra-label until 2004. Currently Metacam is approved for postoperative analgesia in cats as a single subcutaneous dose of 0.3 mg/kg. Repeated administration is not an approved label indication; however, several references discuss its use for multiple days (2). It should be remembered that repeated dosing, especially at the higher label dose has been associated with renal dysfunction in cats. It would seem prudent that repeated dosing be done with full informed consent of the owner with the goal of a careful dose titration to the lowest effective dose.
Carprofen is approved for treatment of perioperative pain and osteoarthritis in dogs. It is not approved for use in cats within the US although it has approved in a number of European countries for many years. Carprofen is effective in cats for control of pain and inflammation; however there is considerable individual variation in the elimination of the drug (3). This can result in accumulation of carprofen with repeated dosing in some cats resulting in toxicity including renal dysfunction and possibly death. If Rimadyl is used, a single dose is preferable. If repeated dosing is attempted a careful individualized safe dose interval should be determined.
Maropitant (Cerenia) has recently been approved for use in dogs as an antiemetic. It is an NK-1 receptor antagonists and appears to interfere with emesis both peripherally and centrally. While not approved for use in cats, it has been used at the same dose as recommended for dogs for the treatment of signs associated with renal failure and other metabolic diseases. Maropitant can be useful for the prevention of emesis associated with opioid and anesthetic administration and should be considered when vomition is contraindicated (e.g., corneal ulcer repair) or when anesthetic recovery is accompanied by significant nausea or vomiting.