The in situ gel formulation of buprenorphine showed sustained drug release for a prolonged period of time. The drug release from RG 502 followed a linear pattern throughout the dissolution without any significant burst release. The amount of buprenorphine released during the first 30 minutes, irrespective of the type of Resomer or dissolution medium, was less than 3%. Drug release continued over 55 days in phosphate buffer and 35 days in Tween 80. The in vitro dissolution method developed during this study was capable of identifying formulation differences and thus will be useful for routine drug delivery research, particularly in situ gel formulation development research. In situ gel formulations are routinely compared using animal models,21, so development of such an in vitro method will expedite formulation evaluation.
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