IN-VITRO CHARACTERIZATION OF POLYMERIC MEMBRANE USED FOR CONTROLLED-RELEASE APPLICATION

The application of a polymer film coat is a common practice in the preparation of controlled release dosage forms. In vitro characterization of the polymeric membrane is essential for optimization of the membrane formulation. Polymers selected in this study were cellulose acetate (CA), ethylcellulose (EC) and copolymers of acrylic and methacrylic esters (Eudragit RL100). Plasticizers used in this study were dibutyl sebacate (DBS), triethyl citrate (TEC) and triacetin. Polymer dispersions containing different plasticizers were cast into membranes on a teflon-coated plate. The resulting membranes were evaluated for permeability and mechanical properties. Membrane permeability was determined by quantifying the transport of a model drug, theophylline, across a circular polymeric membrane mounted in a thermostatted, two-compartment horizontal diffusion cell. Mechanical properties of the membranes, such as tensile strength, percent elongation and modulus of elasticity, were determined using an Instron 4301. The results of this study indicate that the CA and EC membranes were found to be effective in preventing the diffusion of theophylline. The addition of Eudragit RL100 to the CA or EC membranes increased the permeability but decreased the mechanical strength of the resulting membrane(s). A significant increase in permeability was observed at a CA:Eudragit RL100 ratio of 60:40. This could be explained by a change in the mechanism of drug transport, principally from partitioning into the membrane to diffusing through the liquid-filled pores of the resulting membrane(s). The results of the mechanical deformation studies indicate that triacetin has a greater potential for partitioning into the CA polymer than does TEC or DBS. DBS has a greater potential for partitioning into the EC polymer than does TEC or triacetin. The addition of Eudragit RL100 to the CA membrane(s) caused a significant decrease in the tensile strength, percent elongation and modulus of elasticity, thus resulting in weaker and softer membranes. The results indicate that the test methods employed were sufficiently sensitive to quantify the test parameters for the changes in The application of a polymer film coat is a common practice in the preparation of controlled release dosage forms. Since diffusion through a membrane is a simple approach to obtain a predictable release rate, membrane-controlled devices have been widely used. A device for constant release consists of a central reservoir of a drug enclosed by a polymeric membrane that allows the drug to diffuse from the reservoir at predetermined rate. In vitro characterization of the polymeric membrane is essential for optimization of the membrane formulation. In this study, the effects of types of polymers and plasticizers on permeability and mechanical properties of the membranes were evaluated. Cellulosic polymers and copolymers of acrylic and methacrylic esters (Eudragit RL100), which have been widely used as controlled release coating polymers (1-3), were selected for evaluation. Dibutyl sebacate, triethyl citrate and triacetin were used as plasticizers in this study.