Effect of ionic crosslink on the release of metronidazole from partially carboxymethylated guar gum tablet.

Partially carboxymethylated guar gum (PCMGG) was crosslinked in situ by Ca(2+) ions during wet massing step of tablet preparation. The resulting tablets were evaluated for the effect of the extent of crosslinking on drug release and matrix swelling. Increase in the concentration of Ca(2+) ions increased the viscosity of gel layer and reduced the water penetration velocity into the matrix with subsequent decrease in swelling of the tablets and drug release. Beyond a certain concentration of Ca(2+) ions, the viscosity of the gel layer decreased and the drug release rate increased primarily due to erosion of the matrix. The mechanism of drug release appeared to be non-Fickian or anomalous transport. The release data also best fitted in zero order equation. The model drug, metronidazole, was compatible with the matrix materials as evident from instrumental analyses. Such formulation may provide flexibility in achieving the desired drug release rate from crosslinked matrix tablets.