Crosslinked carboxymethylcellulose for the preparation of spherical matrices

Crosslinked carboxymethylcellulose spherical matrices (beads) were prepared by using an in-liquid curing coating process with aluminium chloride as the curing agent. Variously concentrated aqueous solutions of sodium carboxymethylcellulose of three different nominal viscosity grades were used to obtain beans loaded with ambroxol hydrochloride. To characterize the beads their behaviour in,cater was evaluated with respect to preparative variables, i.e. nominal viscosity grade and concentration of the polymer. The swelling process of beads prepared by varying the nominal viscosity grade of sodium carboxymethylcellulose was greatly affected by the presence of the drug and the residual amount of crosslinking agent (free AlCl3). In fact, only by removing the drug and free AlCl3 it was possible to observe that the increase of polymer nominal viscosity grade, Le. molecular rt eight, slowed the early stage of the swelling process. This phenomenon may be explained by increased viscosity of the gel and decreased porosity of the beads. Although the increase of polymer molecular weight reduced matrix porosity it did not modify the drug release process, which occurred rapidly The increase of polymer concentration reduced the residual amount of crosslinking agent. This fact, combined with the greater compactness of the matrix, resulted in a significant decrease in the extent of swelling and in the drug release rate of beads obtained using the highest concentration of the polymer The evaluation of the beads as oral delivery, systems showed that the drug release from beads prepared using the highest concentration,fns rapid in simulated gastric fluid, but extended in simulated intestinal fluid. Moreover in simulated intestinal fluid, a nearly zero-order kinetics was obtained due to the erosion of the swollen matrix. Thus, by development of an appropriate delivery system, a prolonged and constant rate release in the intestinal tr aci may be achieved.