An investigation of formulation factors and processing parameters for the powder-coating of tablets

Dry powder coating of pharmaceutical dosage forms has been investigated as an alternative method to commonly used liquid based coating techniques. Eudragit[trademark] L 100-55 and Eudragit[trademark] L 30 D-55 have been employed in enteric film coatings using aqueous dispersions, organic solutions and compression coating. However, the copolymer has not been investigated in dry powder coating applications. Initially, formulation factors and processing parameters were investigated for the dry powder coating of chlorpheniramine maleate tablets using Eudragit[trademark] L 100-55 as the delayed release polymer. Powder coating was studied as a method to prevent the migration of an ionizable, highly water soluble model drug into the polymeric film during the coating process. Eudragit[trademark] L 100-55 was pre-plasticized with triethyl citrate (TEC) using hot-melt extrusion and subsequently ground into a fine powder. Polyethylene glycol 3350 (PEG 3350) was used as a primer and low melting coating excipient to enhance coating powder adhesion and to improve film formation. The powder coating process was performed in a modified laboratory scale spheronizer. For the dry-powder coating of sodium valproate tablets different subcoating materials were investigated to improve powder adhesion to the substrate and to reduce the level of Eudragit[trademark] L 100-55 required for gastric resistance. PEG 3350 and Methocel[trademark] K4M were incorporated in the Eudragit[trademark] E PO and Eudragit[trademark] RL PO subcoating formulations as pore forming materials. The miscibility of the PEG 3350 and Methocel[trademark] K4M in the film coating was correlated with their ability to function as pore forming agent. The film formation process of thermally cured Eudragit[trademark] L 100-55 dry-powder coatings was characterized. The influence of film additives on relative melt viscosity, surface free energy of the polymer and the mechanical properties of powder-cast films was studied. The influence of Eudragit[trademark] E PO in Eudragit[trademark] L 100-55 film coatings applied by a dry powder coating technique on the drug release mechanism was investigated. Calculation of the Flory-Huggins interaction parameter based on solubility parameters and different analytical techniques demonstrated immiscibility of the copolymers at processing conditions. A broad range of pH dependent theophylline release profiles were obtained as a function of the polymer blend ratio.