Pellets containing an analgesic uniformly dispersed in a lipid carrier such as cholesterol mixed with fatty acid esters, can be used to provide long term pain relief. 5 mg cholesterol-tryglyceride-buprenorphine pellets released the majority of drug in 24-48 hours after implant and provide clinically significant plasma levels of analgesia in mice for 3-9 days. Blood levels of analgesia peak at day-1 and are substantially complete by day-5 depending on the level of buprenorphine. These results demonstrate that post surgical implants provide clinically significant levels of analgesia in the 24-48 hour period following surgery and thus obviate the time consuming, expensive, and high-risk need to inject mice post surgery. The pellets are safe and easy to use. Placed in the surgical wound at the end of surgery, they provide 2-3 days of analgesia and obviate the need for subsequent handling of the animal for pain therapy. The implants have no detectable effect on mouse behavior, hematology, or liver chemistry. The unexpected release kinetics of the 5 mg pellet provides an ideal implant for post surgical analgesia. These implants solve a significant problem facing scientists who use rodents in research and abide by international of animal welfare.
