Preparation of Carbopol/Chitosan Interpolymer Complex as a Controlled Release Tablet Matrix; Effect of Complex Formation Medium on drug Release Characteristics

Chitosan/$Carbopol^{(R)}971NF$ (poly acrylic acid) interpolymer complexes were prepared in pH 3.0, 4.0, and 5.0 medium to control the ratio of chitosan and $Carbopol^{(R)}971NF$ in the interpolymer complex. FT-IR analysis confirmed that the mechanism of complexation involved an electrostatic interaction between the $NH_3^+$ of chitosan and $COO^-$ of $Carbopol^{(R)}971NF$. An increase in the pH of the preparation medium was accompanied by an increase in the ratio of chitosan in the chitosan/$Carbopol^{(R)}971NF$ complex. The maximum yield of interpolymer complexes prepared at pH 3, 4, and 5 (IPC3, IPC4, IPC 5) were obtained at ratios of 1/10, 1/5, and 1/4 (chitosan/$Carbopol^{(R)}971NF$), respectively. At pH 1.2, the overall drug release from IPC tablets did not show significant differences. However, at pH 6.8, the rate of drug release from the IPC5 tablet was higher than that from the IPC4 tablet. The release rate from the IPC3 tablet was observed to increase with time. The release mechanism was increasingly dominated by the relaxational contribution in the order of IPC3, IPC5, and IPC4 at pH 6.8. The diffusional contribution was dominated only in the early stage of drug release and the relaxational contribution gradually increased with time.