Hydrophilic Matrices Geometry, Swelling and Erosion Investigations to Clarify the Release Mechanism

Aim of present work is to study the effect of viscosity and geometry of tablets on swelling, erosion and drug release behavior of matrix tablets of theophylline, a model drug, using natural gums viz. Chitosan [F5], Xanthan [F3], Locust bean gum [F4] and Guar gum [F2] and hydroxypropyl methylcellulose [F1]. Matrix tablets were produced by wet granulation method. The physical characteristics of tablets including geometry of tablets, the swelling and erosion behavior of tablets were studied and the results were correlates with the in vitro drug release. Drug release was proportional to surface area/volume ratio and it was similar for similar surface area/volume ratio. The formulation F5 containing chitosan starts erosion immediately when contacted with dissolution medium and eroded within 5 minutes. Based on the degree of swelling, the formulations arranged as F4>F2>F3>F1 and as per the erosion study the formulations were arrange as F1>F3>F2>F4. These may attributes to polymer viscosities because the formulation F2 (240cp) and F4 (250cp) which showed higher degree of swelling and lower rates of erosion compare to formulation F3 (150cp) and F1 (107cp). Thus, the effect of viscosity and geometry on swelling and erosion behavior of matrix tablets was profound and thus they are significant parameters to study out for the formulation of matrix tablets.