Drug release from film-coated chlorpheniramine maleate nonpareil beads: effect of water-soluble polymer, coating level, and soluble core material.

The purpose of this research was to use a new drug release model to study the effects of formulation parameters on drug release from a film-coated chlorpheniramine (CPM) nonpareil system. The film-coated CPM nonpareils were prepared by using a fluid bed apparatus. A hydroxylpropylmethylcellulose (HPMC) solution was blended with an aqueous ethylcellulose dispersion (Surelease) to adjust the permeability of the film. The apparent permeability of samples was obtained from dissolution data using a previously reported drug release equation. The apparent permeability was plotted versus the film coating level or the HPMC concentration in the film. When the natural logarithm of the apparent permeability versus coating level was graphed, a biphasic plot was observed in the group without HPMC in the film, showing the occurrence of a critical coating level. It was suggested that a mechanically formed porous film (due to an incomplete coating) could change to a nonporous film after the bead was completely coated. However, in the group that contained 12% HPMC in the film, the critical coating level was not observed. A porous film, formed by the leaching out of the water-soluble polymer, would not change to a nonporous film even after the bead is completely coated. Through a mathematical derivation, the decrease of apparent permeability versus coating level was related to the reduction of the total hole area. The apparent permeability was found to increase with the HPMC concentration. After a critical concentration was reached, the further addition of HPMC into the film caused a rapid increase in apparent permeability. The critical HPMC concentration was related to a minimum domain formation concentration (MDFC). A rapid increase of the drug release was observed when the dissolution profile of a sample made from a regular sugar nonpareil core (soluble) was compared with the sample made from a precoated nonpareil core (insoluble), which suggests that the drug release can be enhanced by the dissolution of the core. A minimum concentration of the HPMC was required to effectively modify permeability of the film. The critical coating level and critical concentration of HPMC can be determined from the apparent permeability plot using a previously published equation. The dissolution of a soluble core can greatly enhance the release of the drug from the nonpareil system.