Drug release modulation by physical restrictions of matrix swelling

Swellable matrix systems with anomalous release kinetics are suitable solutions for drug release control for oral administration. Generally, the release rate modulation is achieved through the use of different types of polymer or the employment of soluble or insoluble fillers. The resulting release mechanism depends on the relative importance of tablet relaxation and drug diffusion rates. By adjusting these two rates, it is possible simultaneously to control the release mechanism and the release rate. In this work, we present the results obtained by changing the relaxation rate of the matrix by means of the application of impermeable coatings that partially cover the matrix. The applied impermeable coating modifies the relaxation rate of the matrix by affecting the dimension of the swelling of the plain matrix while leaving the diffusion characteristics of the drug practically intact. The overall result is that the original kinetics of the uncoated matrix is shifted towards constant release, dependent on the extension and position of the impermeable coating.