The Effects of Subcutaneous Ketamine on Postlaparotomy Analgesia and Behavior in Female Sprague–Dawley Rats (Rattus norvegicus)

Multimodal analgesia provides superior pain control compared with single-agent analgesic approaches. However, certain analgesic drug classes such as NSAIDs and opioids may be contraindicated in some studies due to their mechanisms of action, highlighting the need for alternative analgesic options. Little information is available as to the efficacy of alternative supplementary analgesics in laboratory rodents. Here, we investigate the impact of ketamine as an adjunctive analgesic postlaparotomy in 32 female Sprague–Dawley (SD) rats. Rats received either 4 mg/kg Meloxicam in Extended-Release Polymer (Melox-ER) or 1 mg/kg Buprenorphine Base in Extended-Release Polymer (Bup-ER), along with either ketamine (30 mg/kg SC) or volume-matched saline ( n = 8 per treatment group). Postoperative pain behaviors were assessed via video scoring at 30, 90, and 150 min postoperatively, and cage-side evaluations were performed in-person at 3, 6, 12, 24, 32, 48, 56, and 72 h postoperatively. Rat grooming behavior, assessed by the grooming of fluorescent oil from the nape, was evaluated as an indirect method of assessing analgesic efficacy. All rats that received ketamine exhibited higher activity levels, reduced incisional licking, and fewer pain-associated behaviors than nonketamine-treated rats during the initial 90-min postoperative period. Rats that received Melox-ER demonstrated fewer pain-associated behaviors than Bup-ER-treated rats in the acute postsurgical period, regardless of ketamine treatment. Rats treated with Bup-ER took significantly longer to groom fluorescent oil from their fur compared with Melox-ER-treated rats. Our study demonstrates that ketamine confers significant analgesic effects for at least 90 min postoperatively and supports the use of fluorescent oil grooming transfer scores as a method for evaluating postoperative analgesia.