This randomized clinical trial compared postoperative discomfort after onychectomy in cats receiving either transdermal fentanyl (TDF) applied 18 to 24 hours before surgery or intramuscular injection of butorphanol at the time of sedation and at 0, 4, 8, and 12 hours after surgery. Cats were between 2.2 kg (4.84 lb) and 4.3 kg (9.46 lb) and scored for pain at 2, 4, 8, 12, 24, 36, and 48 hours after surgery. Observers were trained and consistent relative to one another and within their own observations. In addition to subjectively scoring pain, investigators measured TDF and butorphanol using plasma cortisol concentration as an objective index. Results indicated that plasma cortisol may not be a consistent measure of analgesic efficacy in cats. It had been hypothesized that TDF would provide more effective and longer lasting analgesia; however, results indicated that both analgesics provided similar relief or lack thereof for 12 hours after surgery. TDF showed a lower pain score only at 8 hours after surgery. The primary advantages for TDF were providing continuous noninvasive delivery that was easy to apply and well tolerated, although subjectively cats in this group were rated as friendlier than cats in the butorphanol group. Its main drawback is that TDF is twice as expensive as butorphanol. 

COMMENTARY: This research compares postoperative discomfort in cats with TDF versus butorphanol and reports that there was not a significant difference in pain relief between the two. Preference and cost would seem to dictate which to use among these choices.

Comparison of transdermal administration of fentanyl versus intramuscular administration of butorphanol for analgesia after onychectomy in cats. Gellasch KL, Kruse-Elliott KT, Osmond CS, Shih ANC, Bjorling DE. JAVMA 220:1020-1024, 2002.