Comparison of the in vitro release characteristics of a wax matrix and a hydrogel sustained release diclofenac sodium tablet

Abstract

Two types of sustained release tablets of diclofenac sodium were formulated, such that one released drug via the pores of a wax matrix (DWM), and the other relied upon the swelling of a hydrogel (DHG). The in vitro release characteristics of these two were compared using USP XXI Dissolution Apparatus I and II as well as an intrinsic dissolution technique at various speeds of rotation. Bnployment of the release exponent ‘n’ as a method of ascertaining the release mode showed that DWM exhibits classic diffusion-controlled release of drug down tortuous pores. This was confirmed by scanning electron microscopy. Release is relatively independent of rotation speed, except when unprotected from abrasion. DHG tablets exhibited near zero-order release, a dynamic equilibrium existing between rate of gel swelling and erosion. This was true up to a point where high rotational speeds upset this equilibrium by increasing erosion. This was confirmed by gel thickness measurements.