Comparative Safety and Efficacy of Extended-Release Buprenorphine Formulations for Mouse Reproductive Surgeries under Tribromoethanol
Extended-release buprenorphine formulations are commonly used to control postoperative pain in rodents with minimal handling-related stress. An FDA-indexed formulation is now available that has been demonstrated safe and effective with ketamine-xylazine and isoflurane anesthesia; however, safe use in combination with tribromoethanol, a nonpharmaceutical-grade anesthetic sometimes favored for short, high-volume procedures, has not been reported. Effects on pregnancy and offspring have also not been examined. In this study we compared the safety and efficacy of the FDA-indexed formulation at the labeled dose (3.25 mg/kg) to the compounded extended-release buprenorphine formulation used by the centralized Transgenic Core at our institution at the manufacturer-recommended dosage (1 mg/kg) in CD-1 mice under tribromoethanol anesthesia. A pilot (n = 5 females per drug) was initially conducted with anesthetic and analgesic in the absence of surgical manipulation, after which the formulations were compared in embryo transfer and vasectomy surgeries (n = 10 males or females per drug). Relative efficacy was assessed at 6, 24, 48, and 72 h after surgery using a cageside ethogram, frequency of rearing behavior compared with baseline, and weight change. No differences were seen between analgesic treatment groups. Safety was evaluated by intraoperative respiratory rate, recovery time, incidence of analgesic injection site lesions, and gross necropsy. Ulceration was only observed at the injection site of mice receiving compounded drug; no other differences between treatments were observed. Effects on pregnancy were evaluated by comparing pregnancy success, litter size, and pup weight at weaning between treatment groups in the initial experiment and embryo transfers subsequently performed by the Transgenic Core (n = 19 sets). No significant differences were identified. These results indicate that both formulations can be safely used in vasectomy and embryo transfer surgeries under tribromoethanol anesthesia; however, the FDA-indexed product may improve welfare by decreasing injection site ulceration compared with the compounded formulation.
Study design showing the anesthesia and five surgical cohorts with data collected for each cohort. Injection site and reproductive success data from the initial experiment were combined with data collected from Transgenic Core surgeries.
(A) Respiratory rates (breaths per minute) under anesthesia for males and females treated with Bup ER or Ethiqa XR 30 min after administration (n = 10 males or 15 females per group). (B) Time to recover righting reflex after TBE injection (n = 10 males or 15 females per group). Lines within violin plot show median and quartiles. *, P ≤ 0.05; †, P ≤ 0.01.
(A) Rearing frequency compared with baseline after ET or vasectomy surgery. (B) Postoperative ethogram scores did not differ by sex or treatment; males and females were combined for analysis. (C and D) Postoperative or post-anesthesia weight change for (C) females or (D) males. For all panels, n = 10 per group except (C), with n = 5 per group. Mean ± SEM is depicted in all panels except (B), which shows median ± IQR. *, P ≤ 0.05 for comparison of rearing between males and females and of weight change in ET compared with sham surgery or TBE-only females.
(A) Left to right: prominent nodule at buprenorphine injection site, excoriation (erythema, scaling, and observed scratching), nodule with ulceration. (B) Percent of mice exhibiting a nodule or erythema on day 3 after buprenorphine injection, or exhibiting ulceration or evidence of excoriation at any time during the observation period. Bup ER n = 23 males and 39 females; Ethiqa XR n = 24 males and 40 females. (C) Survival curve showing injection site nodule duration. Steps represent mice whose nodules resolved. Squares/circles represent mice with unresolved nodules at their experimental endpoint. The number at risk displayed below the survival curve is the number of mice remaining with unresolved nodules at each time point. n = 10 males and 5 females per treatment. Females were only monitored through 18 d. *, P ≤ 0.05; †, P ≤ 0.01.
For all panels, points connected by a line represent two treatment groups from the same IVF. (A) Percentage of ET recipients treated with Bup ER or Ethiqa XR that delivered at least one pup. For n = 9 IVFs, 100% of females in each treatment group had successful pregnancies. (B) Mean number of pups born to recipients in each treatment group. (C) Mean weight of male pups per treatment group. (D) Mean weight of female pups per treatment group. n = 19 IVF sets.
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