The rate of release of drugs decreases
with decrease in solubility of the drugs. It is because the
water dissolves the drug at the surface first, and then penetrates
the matrix via pores, bringing about a gelling of the
polymer. Dissolved drug is then released by diffusion
through the gel and finally the release rate falls as the water
reaches the center due to decreased drug concentration to
less than its solubility (1,21). The solubility of indomethacin
in aqueous medium (phosphate buffer) is very low.
Due to the slow erosion of the matrix and low solubility
the amount of drug released is also less. The value of n
varies from anomalous to near zero order as the solubility
of drugs decreases (