Influence of the viscosity grade and the particle size of HPMC on metronidazole release from matrix tablets

Matrix tablets of metronidazole with hydroxypropyl methylcellulose (HPMC) were prepared by granulation with water and compaction at 127 MPa in a hydraulic press. The release profile of the obtained tablets was evaluated with the USP 23 apparatus 2 (paddle) at 100 rpm and using 0.1 N HCl as the medium. The influence of the HPMC viscosity grade and particle size on the release profile of metronidazole was evaluated at viscosity grades of 15, 860, 5000, 20 000 and 30 000 cP and at particle sizes of 163,213, 335 and 505 μm. The results showed a linear relationship between the inverse of the release rate (Q/t 1/4 ) and the viscosity grade of HPMC, at a HPMC ratio of 10%. A linear relationship between the release rate and the cube of the diameter of the HPMC particles was also observed. Higher HPMC ratios (20 and 30%) showed no difference on release rate when the viscosity and the particle size were changed. An increasing burst effect occurred with increasing viscosity grades and increasing particle sizes of HPMC.