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Abstract Objective: To investigate the relationships between the release rate of drug and the solubility (CSIL) or the diffusion coefficient (DSIL) in silicone elastomer in intravaginal ring (IVR). Methods：The solubilities of progesterone (PGT), gestodene (GEST), and mifepristone (RU486) in silicone elastomer were investigated by the methods of differential scanning calorimetry (DSC). The matrixtype IVR was prepared by injection molding method, and the core of reservoirtype IVR was was the matrixtype IVR, and the controlling sheath was prepared by heating vulcanization method. The release rate of the IVRs in 7 days were tested by in vitro releasing measurement. Results: The solubilities of progesterone, gestodene, mifepristone in MED6382 were 13.06 mg/g, 18.71 mg/g, and 7.5 mg/g, respectively. The cumulative releases of the IVRs carried 300mg drugs in 7 days were progesterone (149.8 mg), gestodene (29.2 mg), mifepristone (15.6 mg), which had showed that the release rates and solubilities of drugs in silicone elastomer had no completely linear relationships. The diffusion coefficient of drug was changed by adding diatomite, chitosan, lactose and isopropyl alcohol, which caused the changes of the release rate and daily release. The diffusions of the drugs were prevented by adding diatomite, lactose and chitosan, which reduced the release rates, but the isopropyl alcohol could promote the drugs to the surface of IVRs, which increased day 1 burst of matrix type vaginal rings . Conclusion: The release rate of drug is determined by both the solubility and the diffusion coefficient of drug in silicone elastomer.In order to regulating the release rates of drugs, the solubilities of drugs in silicone elastomer and the diffusion coefficients influenced by various additives must be considered.
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