Mechanisms to control drug release from pellets coated with a silicone elastomer aqueous dispersion.

The mass transport of two different compounds through polydimethylsiloxane (PDMS)-silica films was investigated to demonstrate qualitatively how this coating system can alter the release of various compounds. Various ratios of PDMS elastomer and silica were used to coat monodisperse particle-sized pellets layered with an ionizable compound (tartrazine) and a nonionized compound (acetaminophen). The 2:1 PDMS-silica composition containing the polyethylene glycol (PEG) 8000 pore former allowed mainly pore transport through void spaces in the PDMS films. Both compounds rapidly diffused through the film as a result of the solubilization and subsequent removal of the PEG 8000 from the film matrix. As the PDMS-silica ratios in the films changed from a 1:1 to a 2:1 to a 4:1 (all without polyethylene glycol 8000) coating formulation, the differences in release rate between acetaminophen and tartrazine changed. The lower ratio of PDMS-silica allowed much faster tartrazine diffusion compared to acetaminophen. As the ratio increased from 1:1 to 2:1, the two compounds were released at similar rates. When the ratio reached 4:1, acetaminophen was released significantly faster than tartrazine. Explanations for these differences and the mechanisms controlling the drug release are discussed in the text. In some circumstances, osmolality and pH affected drug release from dosage forms coated with this polymer system. This study demonstrated that utilization of this polymer system offers a useful tool for the formulation scientist to modify release rates of ionic and nonionic drug substances.