A long-acting buprenorphine delivery system.

A subcutaneously implantable buprenorphine delivery system utilizing cholesterol-glyceryltristearate matrix for prolonged release of drug is described. Implantable cylindrical pellets of buprenorphine (cholesterol 36 mg, glyceryltristearate 4 mg, buprenorphine hydrochloride 10 mg), diameter 3 mm, length 6 mm blocked the antinociceptive action (hot plate, 55 degrees C) of 10 mg kg-1 SC challenge dose of morphine in rats for 12 weeks or more (longer periods not evaluated). The cumulative percent release of buprenorphine from the test devices 2, 4, 6, 10 and 12 weeks after implantation was 27.4, 35.9, 37.6, 39.9 and 43.1, respectively. The release of buprenorphine from 10 mg pellets approximated first-order kinetics with half-lives of 0.85 and 50.24 weeks, for alpha and beta phases, respectively. The test devices possess the desirable characteristics of simplicity, biocompatibility, nontoxicity, ease of sterilization with ethylene oxide, small size for ease of insertion and removal, minimal encapsulation by surrounding tissue and an extended period of drug release unaffected by body metabolism. No side effects were seen in implanted rats which fed well and gained weight during entire treatment. Neither deterioration of implant nor any gross anatomic changes at implant site were apparent 12 weeks after pellet implantation.