Swelling, erosion and release behavior of alginate-based matrix tablets

Hydrophilic matrix tablets based on the alginate system have been used in relation to their possible function in modified drug delivery formulations using metronidazole as a model drug. The matrix tablets were prepared by direct compression using different grades of alginate. The effect of some factors (i.e. particle size of drug, additive used, and pH of medium) on drug release from alginate-based matrix tablets was also investigated. Swelling, erosion, and in vitro release studies of the matrix tablets were carried out in 0.1 N HCl or phosphate buffer (pH 6.8). The alginate-based matrix tablets swelled or eroded while in contact with the aqueous medium and formed a continuous gel layer or underwent combination of swelling and erosion. The swelling action of alginate matrices is controlled by the rate of its hydration in the medium. Different grades of alginate insignificantly influenced the matrix swelling in acidic medium but significantly influenced in neutral medium. The presence of ammonium or calcium salts induced tablet disintegration in acidic medium. However, incorporation of calcium acetate and sodium bicarbonate can alter the tablet swelling in acidic medium. Release studies showed that all investigated factors influence the drug release. The extent of matrix swelling, erosion, and diffusion of drug determined the kinetics as well as mechanism of drug release from alginate-based matrix tablets. Most of the release data in acidic medium showed a good fit into Korsmeyer–Peppas equation but fitted well with zero-order release model, in neutral medium.