Carprofen Attenuates Postoperative Mechanical and Thermal Hypersensitivity after Plantar Incision in Immunodeficient NSG Mice.

Immunodeficient NSG mice are reported to be less responsive to buprenorphine analgesia. Here, we used NSG mice to compare the efficacy of the commonly used dose of carprofen (5 mg/kg) with 5 and 10 times that dose (25 and 50 mg/kg) for attenuating postoperative mechanical and thermal hypersensitivity following an incisional pain model. Male and female NSG mice (n = 45) were randomly assigned to one of 4 groups and received daily subcutaneous injections for 3 d: saline (5 mL/kg), 5 mg/kg carprofen (Carp5), 25 mg/kg carprofen (Carp25), and 50 mg/kg carprofen (Carp50). Mechanical and thermal hypersensitivity were assessed 24 h before and at 4, 24, and 48 h after surgery. Plasma carprofen concentrations were measured in a separate group of mice (n = 56) on days 0 (at 2, 4, 12, and 23 h), 1, and 2 after the first, second, and third doses, respectively. Toxicity was assessed through daily fecal occult blood testing (n = 27) as well as gross and histopathologic evaluation (n = 15). Our results indicated that the saline group showed both mechanical and thermal hypersensitivity throughout the study. Carp5 did not attenuate mechanical or thermal hypersensitivity at any time point. Carp25 attenuated mechanical and thermal (except for the 4-h time point) hypersensitivity. Carp50 attenuated only thermal hypersensitivity at 24 h. Fecal occult blood was detected in 1 of 8 Carp25-treated mice at 48 and 72 h. Histopathologic abnormalities (gastric ulceration, ulcerative enteritis, and renal lesions) were observed in some Carp50-treated mice. Plasma carprofen concentrations were dose and time dependent. Our results indicate that Carp25 attenuated postoperative mechanical and thermal hypersensitivity more effectively than Carp5 or Carp50 in NSG mice with incisional pain. Therefore, we recommend providing carprofen at 25 mg/kg SID for incisional pain procedures using immunodeficient NSG mouse.

Comparing Three Formulations of Buprenorphine in an Incisional Pain Model in Mice.

This study compared the therapeutic effects in mice of 3 different formulations of buprenorphine. These formulations were standard buprenorphine hydrochloride (Bup-HCL) and 2 different extended-release buprenorphine formulations (Bup-ER and Ethiqa-XR [Bup-XR]). Drugs were evaluated based on their ability to attenuate thermal hypersensitivity in a mouse plantar incisional pain model. We hypothesized that Bup-HCL would attenuate postoperative thermal hypersensitivity at 20 min after administration, and that Bup-ER and Bup-XR would attenuate thermal hypersensitivity at 40 min after administration. Male C57BL6/J mice were randomly assigned to 1 of 4 treatment groups: 1) saline, 5 mL/kg SC, once; 2) Bup-HCL, 0.1 mg/kg SC, once; 3) Bup-ER, 1 mg/kg, SC, once; and 4) Bup-XR, 3.25 mg/kg, SC, once. Thermal hypersensitivity was assessed on the day before surgery and again on the day of surgery at 20, 40, 60, 90, and 120 min after drug administration. Thermal hypersensitivity after surgery was not different among the Bup-HCL, Bup-ER and Bup-XR groups at any timepoint. In addition, all buprenorphine treatment groups showed significantly less thermal hypersensitivity after surgery than did the saline group. Subjective observations suggested that mice that received Bup-ER or Bup-XR became hyperactive after drug administration (83 and 75% of mice tested, respectively). Our results indicate that Bup-HCL, Bup-ER, or Bup-XR attenuate thermal hyper- sensitivity related to foot incision by 20 min after administration.

Efficacy of Supplemental Diet Gels for Preventing Postoperative Weight Loss in Mice ( Mus musculus).

This study investigated whether the use of commercially available diet gels prevented the postoperative weight loss associated with major survival surgery in mice. C57BL/6 mice were divided into 3 groups ( n = 9 per group) that received moistened chow pellets alone or with one of 2 commercially available diet gels. Mice began receiving the test diets 3 d before surgery (baseline) and were weighed daily for 7 d after surgery. On day 0, mice underwent ventral midline laparotomy, during which the intestines were manipulated for 2 min and a segment of jejunum was briefly clamped. Compared with the baseline value for the same group, body weights for the mice that received moistened chow only were significantly lower on all postoperative days (days 1 through 7). In contrast, body weights of mice that received both moistened chow and diet gel differed from baseline only on days 2 and 3 for one product and were never different from baseline for the other product. This study indicates that the combination of diet gel and moistened chow prevented or mitigated postoperative weight loss after a laparotomy procedure in mice.

Effectiveness of two extended-release buprenorphine formulations during postoperative period in neonatal rats.

Information on the effectiveness of a new long-lasting buprenorphine formulation, extended-release buprenorphine, in the neonatal rat is very limited. This study compares whether a high dose of extended-release buprenorphine (XR-Hi) attenuates thermal hypersensitivity for a longer period than a low dose of extended-release buprenorphine (XR-Lo) in a neonatal rat incisional pain model. Two experiments were performed. Experiment one: Male and female postnatal day-5 rat pups (n = 38) were randomly assigned to 1 of 4 treatment groups and received a subcutaneous administration of one of the following: 1) 0.9%NaCl (Saline), 0.1 mL; 2) sustained release buprenorphine (Bup-SR), 1 mg/kg; 3) XR-Lo, 0.65 mg/kg; and 4) XR-Hi, 1.3 mg/kg. Pups were anesthetized with sevoflurane in 100% O2 and a 5 mm long skin incision was made over the left lateral thigh and underlying muscle dissected. The skin was closed with surgical tissue glue. Thermal hypersensitivity testing (using a laser diode) and clinical observations were conducted 1 hour (h) prior to surgery and subsequently after 1, 4, 8, 24, 48, 72 h of treatment. Experiment two: The plasma buprenorphine concentration level was evaluated at 1, 4, 8, 24, 48, 72 h on five-day-old rat pups. Plasma buprenorphine concentration for all treatment groups remained above the clinically effective concentration of 1 ng/mL for at least 4 h in the Bup-SR group, 8 h in XR-Lo and 24 h in XR-Hi group with no abnormal clinical observations. This study demonstrates that XR-Hi did not attenuate postoperative thermal hypersensitivity for a longer period than XR-Lo in 5-day-old rats; XR-Hi attenuated postoperative thermal hypersensitivity for up to 4 h while Bup-SR and XR-Lo for at least 8 h in this model.

Efficacy of 3 Buprenorphine Formulations for the Attenuation of Hypersensitivity after Plantar Incision in Immunodeficient NSG Mice.

Buprenorphine is perhaps the most prescribed analgesic for management of postoperative pain in mice. Although various buprenorphine formulations are effective in commonly used immunocompetent mouse strains, a knowledge gap exists regarding its efficacy in immunodeficient mice. Here we used a plantar incision to evaluate the efficacy of 3 buprenorphine formulations for attenuating postoperative mechanical and thermal hypersensitivity in the immunodeficient NSG mouse strain. We also characterized the pharmacokinetics of these formulations over a 72-h period. We hypothesized that all 3 buprenorphine formulations evaluated-the standard preparation and 2 extended-release products (Bup-HCl, Bup-ER, and Bup-XR, respectively)-would attenuate postoperative mechanical and thermal hypersensitivity resulting from a plantar incision in NSG mice. Male and female NSG mice (n = 48) were allocated to 4 treatment groups: saline (0.9% NaCl, 5 mL/kg SC once); Bup-HCl (0.1 mg/kg SC, BID for 2 d); Bup-ER (1.0 mg/kg SC once); and Bup-XR (3.25 mg/kg SC once). Mechani- cal and thermal hypersensitivity assessments were conducted 24 h before surgery and at 4, 8, 24, 48, and 72 h afterward. All groups of mice showed mechanical and thermal hypersensitivity within the first 24 h after surgery. Behavioral pain indicators (guarding, toe-touching [intermittent partial weight bearing], licking the incision, vocalizations) were observed in some mice from each group at every postoperative time point. Plasma buprenorphine was measured in a separate group of mice and concentrations surpassed the suggested therapeutic level (1.0 ng/mL) for less than 4 h for Bup-HCl, for at least 24 h for Bup-ER, and for 72 h for Bup-XR. Our results indicate that at the dosages studied, these buprenorphine formulations do not adequately attenuate postoperative mechanical and thermal hypersensitivity in the plantar incisional model in NSG mice. These findings support the need for strain-specific analgesic protocols for mice used in research.

Extended-release Buprenorphine, an FDAindexed Analgesic, Attenuates Mechanical Hypersensitivity in Rats (Rattus norvegicus).

A new extended-release buprenorphine (XR), an FDA-indexed analgesic, has recently become available to the laboratory animal community. However, the effectiveness and dosing of XR has not been extensively evaluated for rats. We investigated XR's effectiveness in attenuating postoperative hypersensitivity in a rat incisional pain model. We hypothesized that high dose of XR would attenuate mechanical and thermal hypersensitivity more effectively than the low dose of XR in this model. We performed 2 experiments. In experiment 1, male adult Sprague-Dawley rats (n = 31) were randomly assigned to 1 of the 4 treatment groups: 1) saline (saline, 0.9% NaCl, 5 mL/kg, SC, once); 2) sustained-release buprenorphine (Bup-SR; 1.2 mg/kg, SC, once), 3) low-dose extended-release buprenorphine (XR-Lo; 0.65 mg/kg, SC, once), and 4) high-dose extended-release buprenorphine (XR-Hi; 1.3 mg/kg, SC, once). After drug administration, a 1 cm skin incision was made on the plantar hind paw under anesthesia. Mechanical and thermal hypersensitivity were evaluated 1 d before surgery (D-1), 4 h after surgery (D0), and for 3 d after surgery (D1, D2, and D3). In experiment 2, plasma buprenorphine concentration (n = 39) was measured at D0, D1, D2, and D3. Clinical observations were recorded daily, and a gross necropsy was performed on D3. Mechanical and thermal hypersensitivity were measured for 3 d (D0-D3) in the saline group. Bup-SR, XR-Lo, and XR-Hi effectively attenuated mechanical hypersensitivity for D0-D3. Plasma buprenorphine concentrations remained above 1 ng/mL on D0 and D1 in all treatment groups. No abnormal clinical signs were noted, but injection site reactions were evident in the Bup-SR (71%), XR-Lo (75%), and XR-Hi (87%) groups. This study indicates that XR-Hi did not attenuate hypersensitivity more effectively than did XR-Lo in this model. XR 0.65 mg/kg is recommended to attenuate postoperative mechanical hypersensitivity for up to 72 h in rats in an incisional pain model.