Direct Compression Controlled Release Tablets Using Ethylcellulose Matrices

Controlled release erodible matrix tablets were manufactured by a simple, direct compression process using ethylcellulose alone as the matrix former. Each of four different viscosity grades of ethylcellulose (10, 20, 45 and 100 cp) was dry mixed with either indomethacin or theophylline and a small amount of lubricant, then directly compressed into tablets. In initial trials, compression force was held constant, resulting in tablets of varying hardness. In a second study, the compression force was varied to produce tablets of equal hardness. Lower viscosity grades of ethylcellulose were more compressible than higher viscosity grades, allowing production of harder tablets for a given drug. Harder tablets resulted in controlled release of the drug over a longer time period. Dissolution studies indicated that tablet hardness is more important in determining dissolution rate than is the polymer viscosity grade. A mathematical model combining diffusion and erosion mechanisms was developed to describe drug release. Improved r² values over pure diffusion, erosion and diffusion/relaxation models were obtained. Examination of residuals indicated that the derived composite model was more appropriate for the data