Wax-based sustained release matrix pellets prepared by a novel freeze pelletization technique I. Formulation and process variables affecting pellet characteristics.

A novel freeze pelletization technique was evaluated for the preparation of wax-based matrix pellets. Pellets containing either theophylline or diltiazem HCl were prepared using various waxes. In this technique, molten waxes along with a dispersed active ingredient were introduced as droplets into an inert and immiscible column of liquid to form pellets. An 80% (w/w) aqueous glycerol solution was found to be the most suitable column liquid for preparing spherical wax pellets. The physical stability of the molten wax suspensions was substantially improved by the addition of a 5% (w/w) colloidal silica gel. Pellet size obtained was directly proportional to the cubic root of the outer radius of the needle tip used to form pellets. Pellet size increased as the ratio of interfacial tension (gamma(LL)) to the density difference (Deltarho) between the molten matrix and the column liquid increased. Moreover, an increase in the drug load of theophylline increased the pellet size. However, an addition of a surfactant to the matrix slightly decreased the pellet size. Microscopic studies indicated that theophylline was homogenously dispersed throughout the matrix and existed in a crystalline state at higher drug loads. The percent drug recoveries ranged from 90.7 to 102.3% with acceptable drug loads up to 20% (w/w). Therefore, wax pellets containing drugs of varying aqueous solubility were successfully prepared using this technique.