Investigation of the release behavior of a covered-rod-type formulation using silicone

The purpose of this study was to investigate the effects of the properties of a drug on its release behavior in a cylindrical sustained-release formulation having a two-component structure, with a silicone matrix containing drug powder as the inner layer component, and with its lateral side covered with an silicone outer layer (CR silicone formulation). In this study, the release profile of a drug from "the lateral side covered with silicone" and from "the cross-sections where the inner layer is exposed to the surface" was examined using a newly designed bi-directional elution cell. The relationships between the release profile and solubility of the drug and its permeability through silicone were also studied. Bovine serum albumin (BSA), antipyrine (ANP), indometacin (IDM) and ketoprofen (KP) were used as model drugs. Each CR silicone formulation containing drug powder consisting of a drug and sucrose (SUC) was investigated, and a satisfactory relationship was observed between drug release from the cross-sections and drug solubility, and between drug release from the lateral side and permeability of the drug through a silicone membrane. For CR silicone formulations containing IDM, the addition of deoxycholate sodium (DOC) improved the solubility of IDM; however, release from the lateral side of the formulation remained unchanged, and IDM release from the cross-sections of the formulation increased. In this study it was found that, for controlled release of a drug from CR silicone formulations, control of drug solubility is effective.