Phospholipid-encapsulated bupivacaine and analgesia after onychectomy in cats

The purpose of this investigation was to compare the analgesic effectiveness of a long‐acting phospholipid‐encapsulated microcrystalline bupivacaine (PMB) preparation to butorphanol after onychectomy in cats. After obtaining informed owner consent and after physical examination, cats were randomly assigned to one of the two treatment groups: butorphanol (BUT, 0.4 mg kg−1 IM; n = 22) or local injection/application of PMB (5 mg kg−1; n = 23). Prior to surgery and at 0, 0.5, 1, 2, 4, 8, and 24 hours after trachael extubation, heart rate, respiratory rate, rectal temperature were obtained, and a single observer blinded to treatment assessed pain, lameness, trachael sedation and temperament. Owners assessed pain in their cats approximately 48 and 72 hours after trachael extubation. All cats were given acepromazine (ACE, 0.025 mg kg−1), BUT (0.2 mg kg−1), ketamine (5 mg kg−1) and glycopyrrolate (0.01 mg kg−1) IM and anesthesia was induced and maintained with isoflurane in O2. Front‐limb onychectomy was performed by disarticulating P3 using sharp dissection with a scalpel. Nine cats in the BUT group and two in the PMB group were also simultaneously castrated. BUT or PMB was administered, and the front limbs were bandaged. Acepromazine or BUT were administered as necessary to treat pain or dysphoria in the postoperative period. A RM anova and Wilcoxon rank sum test were used to analyze physiologic and categorical data, respectively. There was decreased requirement for ACE and/or BUT in the postoperative period for PMB cats (1.3 ± 1 doses 24 hours−1 (mean ± SD) for BUT versus 0.6 ± 0.6 doses 24 hours−1 for PMB), and overall pain score was better in the PMB group. Behavior score at extubation was also better in the PMB group. Lameness at 24 hours was not different between groups, and owners' assessment of postoperative pain was not different between groups. The local injection of PMB resulted in improved analgesia and a decreased requirement for postoperative pain medication in the early postoperative period.