Systemic analgesics, such as opioids and nonsteroidal anti-inflammatory drugs, may be contraindicated in certain studies due to their mechanisms of action and risk for systemic effects. Local anesthetics (LAs) are therefore crucial in managing postoperative pain, potentially decreasing the need for systemic analgesics. However, the utility of standard formulation LAs is limited by their short duration. This study evaluated the use of a commercially available extended-release (XR) liposomal bupivacaine (LB) in a mouse paw incisional model. Our goal was to assess whether LB attenuates postoperative mechanical hypersensitivity (MH) and thermal hypersensitivity (TH). Adult female and male C57BL/6NCrl mice were randomly assigned to one of 3 groups: (1) 5 mg/kg SC meloxicam plus 3.25 mg/kg SC XR-buprenorphine (MELOX/XR-BUP); (2) 2 mg/kg intraincisional standard bupivacaine (SB); or (3) 6 mg/kg intraincisional LB. MH and TH were assessed on days -1 (baseline), 0 (2 hours postoperatively), 1, 2, 3, and 4 using von Frey and Hargreaves testing, respectively. Hind paw incisional surgery was performed on day 0. Both the MELOX/XR-BUP and SB groups demonstrated significant attenuation of MH on all postoperative days compared with baseline, while the LB group showed significant attenuation of MH on days 1-4. In the MELOX/XR-BUP group, there was a significant reduction in TH on days 1-3. In both the SB and LB groups, there was no significant reduction in TH across all postoperative days. Together, these data suggest that a single 6-mg/kg intraincisional dose of LB in C57BL/6NCrl mice does not attenuate TH over a 4-day postoperative period but does attenuate MH on postoperative days 1-4 in our incisional model. In comparing the treatments, we conclude that the relative ability of LB to attenuate postoperative MH and TH was inferior to that of MELOX/XR-BUP and comparable to that of SB in a mouse paw incisional model.
Wang et al. (Fri,) studied this question.