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

The application of a polymer film coat is a common practice in the pre paration of controlled release dosage forms. In vitro characterization of the polymeric membrane is essential for optimization of the membra ne formulation. Polymers selected in this study were cellulose acetate (CA), ethylcellulose (EC) and copolymers of acrylic and methacrylic e sters (Eudragit RL100). Plasticizers used in this study were dibutyl s ebacate (DBS), triethyl citrate (TEC) and triacetin. Polymer dispersio ns containing different plasticizers were cast into membranes on a tef lon-coated plate. The resulting membranes were evaluated for permeabil ity and mechanical properties. Membrane permeability was determined by quantifying the transport of a model drug, theophylline, across a cir cular polymeric membrane mounted in a thermostatted, two-compartment h orizontal diffusion cell. Mechanical properties of the membranes, such as tensile strength, percent elongation and modulus of elasticity, we re determined using an Instron 4301. The results of this study indicat e that the CA and EC membranes were found to be effective in preventin g the diffusion of theophylline. The addition of Eudragit RL100 to the CA or EC membranes increased the permeability but decreased the mecha nical 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, pr incipally 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 p otential for partitioning into the CA polymer than does TEC or DBS. DB S has a greater potential for partitioning into the EC polymer than do es TEC or triacetin. The addition of Eudragit RL100 to the CA membrane (s) caused a significant decrease in the tensile strength, percent elo ngation and modulus of elasticity, thus resulting in weaker and softer membranes. The results indicate that the test methods employed were s ufficiently 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 throug h a membrane is a simple approach to obtain a predictable release rate , membrane-controlled devices have been widely used. A device for cons tant release consists of a central reservoir of a drug enclosed by a p olymeric membrane that allows the drug to diffuse from the reservoir a t predetermined rate. In vitro characterization of the polymeric membr ane is essential for optimization of the membrane formulation. In this study, the effects of types of polymers and plasticizers on permeabil ity and mechanical properties of the membranes were evaluated. Cellulo sic polymers and copolymers of acrylic and methacrylic esters (Eudragi t RL100), which have been widely used as controlled release coating po lymers (1-3), were selected for evaluation. Dibutyl sebacate, triethyl citrate and triacetin were used as plasticizers in this study.