Purpose: To comparatively evaluate the effect of two hydroxylpropyl methylcellulose (HPMC) molecular weight grades (K4M and K15M) on drug release from diclofenac sodium matrix tablets.

Methods: Tablets containing diclofenac sodium were prepared by direct compression method at various drug/HPMC ratios and evaluated in vitro for their water uptake, erosion and dissolution characteristics over a period of 8 h. Their release data were analyzed according to various release kinetic models.

Results: The release rate of diclofenac decreased with increase in polymer content and was dependent on the HPMC type used, with the lower release rate observed in formulations containing the higher molecular weight grade HPMC K15M. Formulations containing the higher molecular weight HPMC (F4, F5 and F6) showed higher water uptake than those containing the lower molecular weight polymer (F1, F2 and F3) (p < 0. 001). The formulations incorporating the lower molecular weight HPMC K4M (F1, F2 and F3) showed higher erosion than those that contained HPMC K15M (F4, F5 and F6) (p < 0.001). Kinetic data based on the release exponent, n, in Peppas model, showed that n values were between 0.14 and 0.55, indicating that drug release from HPMC matrices was predominantly by diffusion.

Conclusion: This study demonstrates that the molecular weight (MW) of HPMC does affect the water uptake and erosion as well as the rate of drug release from of HPMC matrices.

Keywords: Matrix, Diclofenac sodium, HPMC, Erosion, Water uptake.