Adequate pain management is essential for ethical and scientific reasons in animal experiments and should completely cover the period of expected pain without the need for frequent re-application. However, current depot formulations of Buprenorphine are only available in the USA and have limited duration of action. Recently, a new microparticulate Buprenorphine formulation (BUP-Depot) for sustained release has been developed as a potential future alternative to standard formulations available in Europe. Pharmacokinetics indicate a possible effectiveness for about 72 h. Here, we investigated whether the administration of the BUP-Depot ensures continuous and sufficient analgesia in two mouse fracture models (femoral osteotomy) and could, therefore, serve as a potent alternative to the application of Tramadol via the drinking water. Both protocols were examined for analgesic effectiveness, side effects on experimental readout, and effects on fracture healing outcomes in male and female C57BL/6N mice. The BUP-Depot provided effective analgesia for 72 h, comparable to the effectiveness of Tramadol in the drinking water. Fracture healing outcome was not different between analgesic regimes. The availability of a Buprenorphine depot formulation for rodents in Europe would be a beneficial addition for extended pain relief in mice, thereby increasing animal welfare.

Adequate pain management is essential for ethical and scientific reasons in animal experiments and should completely cover the period of expected pain without the need for frequent re-application. However, current depot formulations of Buprenorphine are only available in the USA and have limited duration of action. Recently, a new microparticulate Buprenorphine formulation for sustained release has been developed and safely used in first studies serving as an alternative product within Europe. Pharmacokinetics indicate a potential effectiveness for about 72h; the period that must be covered with analgesia in mouse fracture models. Here, we investigated whether the administration of the newly developed sustained-release Buprenorphine formulation ensures a continuous and sufficient analgesia in mouse femoral fracture models as a potent alternative to the application of Tramadol via drinking water. Both protocols were examined for analgesic effectiveness and side effects on experimental readout in two femoral fracture models using rigid and flexible external fixators in male and female C57BL/6N mice. We monitored general parameters of wellbeing, and model-specific pain parameters. Both, Tramadol in the drinking water and the sustained-release Buprenorphine provided effective analgesia. However, in male mice with flexible fixation, composite pain scores were significantly higher with Tramadol than in the other groups, and locomotion during gait analysis was more profoundly altered. Fracture healing outcome was not different between analgesic regimes. The availability of a sustained-release formulation of Buprenorphine in Europe would be beneficial for pain management in preclinical studies to increase animal welfare and actively support the refinement of painful animal experiments.