Injection-site Reactions to Sustained-release Meloxicam in Sprague-Dawley Rats

Comparison of Systemic Extended-release Buprenorphine and Local Extended-release Bupivacaine-Meloxicam as Analgesics for Laparotomy in Mice

Extended-release (ER) local anesthetics can be used in multi-modal analgesia or in situations in which systemic analgesics may alter animal physiology and thus introduce interpretational confounds. In this study, we compared the analgesic efficacy of an ER buprenorphine formulation with that of a synergistic combination of ER bupivacaine and meloxicam. Female and male CD1 mice were randomly assigned to receive subcutaneous buprenorphine (3.25mg/kg) preemptively, subcutaneous infiltration of bupivacaine???meloxicam (0.03mL at incision closure (bupivacaine, 35mg/kg; meloxicam, 1mg/kg), or saline (10mL/kg SC) after induction of anesthesia. After laparotomy, mice were assessed for changes in daily body weight, rearing frequency, nest consolidation scores, time-to-integrate-nest test (TINT), and response to von Frey testing at 4, 8, 24, 48, and 72h after surgery. Daily weight, nest consolidation scores and rearing frequency were not significantly different among the 3 groups. TINT had fallen significantly response at 24 and 48h after injection in the ER buprenorphine group as compared with the saline and ER bupivacaine-meloxicam groups. Nociceptive thresholds, as assessed with von Frey testing, differed between saline controls and both analgesic groups at 4, 8, 24, 48, and 72 h after surgery. None of the mice in the bupivacaine???meloxicam group developed signs of neurotoxicity, a potential side effect of high-dose local anesthetics. This study demonstrates that local ER bupivacaine???meloxicam may be a useful alternative to systemic, ER buprenorphine for the relief of pain after laparotomy in mice.

Treatment of Pain in Rats, Mice, and Prairie Dogs

Recent myomorph and scuiromorph rodent analgesia studies are reviewed and evaluated for potential clinical application. Differences between laboratory animal studies and clinical use in diseased animals are discussed. Analgesia classes reviewed include local anesthetics, nonsteroidal anti-inflammatories, acetaminophen, opioids, and adjuvants such as anticonvulsants. Routes of administration including sustained-release mechanisms are discussed, as are reversal agents. Drug interactions are reviewed in the context of beneficial multimodal analgesia as well as potential adverse effects. Dosage recommendations for clinical patients are explored.

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.

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.