FICKIAN AND RELAXATIONAL CONTRIBUTION QUANTIFICATION OF DRUG-RELEASE IN A SWELLABLE HYDROPHILIC POLYMER MATRIX

Hydroxypropylmethylcellulose (HPMC) is becoming very popular in the formulation of controlled release tablets, mainly because of its hydrophillic and swelling properties. In HPMC tablet matrix systems, the drug release occurs mainly by Fickian diffusion and by polymer relaxation. The amount of drug released by these two phenomena was quantified by applying a heuristic model recently proposed. Recent studies show that it is possible to modify the kinetics of drug release by restricting matrix swelling. The aim of this study is to present some new evidence that tends to confirm these findings and to quantify the Fickian and case II relaxational contribution of drug release by using a PCNONLIN computer software package. Results obtained show a direct relationship between releasing areas and the amount of drug dissolved. Tablets with matrix swelling restrictions exhibit a shift towards drug release by relaxational mechanism, which makes this technique a useful tool when a shift towards constant drug release is desired.