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

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.