Influence of processing and curing conditions on beads coated with an aqueous dispersion of cellulose acetate phthalate.

The influence of fluidized-bed processing conditions, as well as curing parameters with and without humidity, on drug release from beads coated with cellulose acetate phthalate (CAP) aqueous dispersion was investigated. Theophylline beads prepared by extrusion-spheronization were coated with diethyl phthalate (DEP)-plasticized CAP dispersion (Aquacoat CPD) using a Strea-1 fluidized-bed coater. The parameters investigated were plasticizer level, outlet temperature, spray rate during coating application and fluidizing air velocities using a half-factorial design. The processing temperature during coating applications was identified as a critical factor among the variables investigated. The release rate significantly decreased when the beads were coated at 36 degrees C compared to those coated at 48 degrees C (P<0.01). Higher coating efficiencies and better coalescence of films were obtained at the lower coating temperature. Above the minimum film-formation temperature (MFFT), drug release in acid decreased as the coating temperature was decreased. Curing at 60 degrees C significantly reduced the drug release for beads coated at 32 degrees C, but had no significant effect on drug release for beads coated at temperatures above 36 degrees C. Curing at 50 degrees C in an atmosphere containing 75% RH (relative humidity), irreversibly converted poor film formation into better coalescence, and increased the mechanical toughness of films. Subsequent removal of the moisture absorbed from beads did not significantly alter the enteric profiles obtained through heat-humidity curing. The extent of coalescence via heat-humidity curing was dependent on the curing temperature, % humidity, curing time and coating temperature. The results demonstrated the importance of the selection of coating temperature for CAP-coated beads and the role of moisture on CAP film formation. Curing with humidity was found to be more effective than without.