Analgesia after onychectomy in cats - Veterinary Medicine
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Analgesia after onychectomy in cats
Providing pain relief after onychectomies in cats is a must, and you have many options. Choosing which drug to use can be confusing, but, in general, a multimodal approach seems best.


The most common opioid analgesics studied in cats include butorphanol, buprenorphine hydrochloride, fentanyl, and morphine. One study found that butorphanol (0.4 mg/kg intravenously at extubation and subcutaneously every four hours postoperatively) subjectively provided significantly better analgesia over the control group in cats that had undergone onychectomy.3 Buprenorphine is a partial agonist that also has limited side effects; however, the analgesic effects may also have a maximum limit despite increasing doses.8,9 Another disadvantage is that it has a relatively slow onset of action of about one hour.8,9,29 Another study that used subjective pain scoring and cortisol concentrations within 12 hours of surgery found that buprenorphine (0.01 mg/kg intramuscularly) was significantly more effective at pain relief at four hours than oxymorphone (0.05 mg/kg intramuscularly), ketoprofen (2 mg/kg intramuscularly), and saline solution in cats.4 The dose may be important since in a similar study ketoprofen given at a dose of 2 mg/kg intramuscularly outperformed buprenorphine given at a dose of 0.006 mg/kg intramuscularly.29 In another study, buprenorphine (0.01 mg/kg intramuscularly), morphine (0.2 mg/kg intramuscularly), and butorphanol (0.2 mg/kg intramuscularly) raised the thermal threshold of cats, but no difference in degree of temperature tolerated was found among the groups.30 However, buprenorphine and morphine displayed analgesic effects four hours or more after administration, whereas butorphanol had almost immediate effects.30 The analgesic effect of butorphanol and morphine lasted only two hours compared with eight hours provided by buprenorphine.30 These findings are similar to those of another study in which buprenorphine provided better analgesia than morphine more than two hours after administration.31 One study reports the advantage of combining hydromorphone (0.1 mg/kg intramuscularly) and butorphanol (0.4 mg/kg intramuscularly) to increase the duration of action of both drugs.32 Analgesia was decreased over hydromorphone alone, but the duration of action was measured up to nine hours.32

Transdermal fentanyl patches (25 g/hr) have the advantage of being easily applied; however, a large variation exists in blood fentanyl concentrations among cats, and patches must be applied several hours in advance.5,8,9,16 In a critical review in which several pharmacokinetic studies were compared, it was recommended that the patch be applied seven hours before surgery. The dose recommendation was one 25-g/hr patch per cat or kitten.28 Studies comparing butorphanol and fentanyl in cats after onychectomy have yielded mixed results.3,4,7,16,18 In one study, cats that received transdermal fentanyl after onychectomy had lower subjective pain scores eight hours after surgery than those that received butorphanol, although both groups had significantly lower mean plasma cortisol concentrations after surgery than before.7 In contrast, another study found that there was no difference in the analgesic effect between fentanyl and butorphanol with subjective evaluation as well as standing foot pressure.16 Recently, gait analysis on unilaterally declawed cats was used to compare butorphanol and transdermal fentanyl after onychectomy.18 All cats were significantly lamer postoperatively with no difference between protocols 24 hours after surgery.18 Forty-eight hours after surgery, cats receiving fentanyl or butorphanol were significantly less lame than those receiving topical bupivacaine. Additionally, cats receiving butorphanol were more lame on Day 2 than those receiving fentanyl based on a ratio calculated for the peak vertical force of the affected leg to the combined peak vertical forces of the remaining three limbs.18 On Days 3 and 12 no significant differences between the groups were present; however, even 12 days after surgery the cats had not returned to normal function.18 This delayed return to normal function may mean that analgesic therapy should be continued past the initial postoperative period. Likely, the length of recovery after onychectomy has been underestimated because of bilateral surgeries.


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