Investigation of the influence of mean HPMC particle size and number of polymer particles on the release of aspirin from swellable hydrophilic matrix tablets.

The effects of hydroxypropyl methylcellulose (HPMC) of different particle size ranges, size distributions and concentrations on the release behaviour of aspirin from a swellable matrix tablet system were studied. A mean HPMC (Methocel K15M Premium) particle size of 113 microm was identified as a critical threshold in this study. Drug release rate increased markedly when polymer particle size was increased above 113 microm. Release rate was much less sensitive to changes in particle size below 113 microm. Aspirin release mechanism followed first order kinetics where mean HPMC particle size was below 113 microm. Release mechanism deviated from first order kinetics when the mean particle size was above 113 microm. Polymer fractions with similar mean particle size but differing size distribution were also observed to influence drug release rate but not release mechanism. First order release constant K(1) was found to be quantitatively related to the reciprocal of the cube root of both mean polymer particle size and number of polymer particles in the matrix.