The influence of Eudragit type on the dissolution rate of acetylsalicylic acid from matrix tablets.

The effect of four Eudragits used as matrix substances on the physical characteristics of tablets and on the dissolution rate of acetylsalicylic acid has been investigated. The concentration of matrix substance necessary for achieving the appropriate effect of sustained release of acetylsalicylic acid (ASA) depends on the type of Eudragit used. For tablets prepared using Eudragit RS-100, Eudragit L-100-55 and Eudragit S-100, the acceptable dissolution rate of ASA was obtained with only 3% of polymer. In the case of Eudragit RL-100, to obtain the same effect, 10% of polymer was required. The dissolution data were evaluated on the basis of theoretical dissolution equations and by linear transformation of dissolution curves. The following mathematical models were employed: zero order equation, first order kinetics, Hixon-Crowell's cube root kinetics and diffusion model. The results indicated that the fitness of the kinetic model was dependent on the type of Eudragit used.