Abstract

Five different formulations of naproxen sodium core tablets were prepared using different amounts of Methocel K15M CR by direct compression method. From a particular formulation, 50 % of tablets were kept uncoated and enteric coating was applied to the remaining 50 % using cellulose acetate phthalate (6 % w/w). Dissolution, swelling and erosion tests of uncoated tablets were conducted 8 hours in phosphate buffer (pH 7.4). For enteric coated tablets, dissolution test was performed for first 2 hours in acidic medium (pH 1.2) then 8 hours in phosphate buffer (pH 7.4). Enteric coating was able to prevent the disintegration of the matrix tablets and dissolution of naproxen in the acidic medium. In the buffer medium, irrespective of the presence or absence of enteric coating, higher percentage of Methocel K15 MCR increased swelling of the tablets in first few hours which was followed by erosion of the tablet matrix. Dissolution studies revealed that high percentage of Methocel K15M CR retarded the release of naproxen for a longer period of time. Taking the swelling and erosion pattern and dissolution data together we concluded that with the increase of hydrophilic polymer content, the release mechanism of naproxen shifted towards swelling and erosion dependent processes.