Influence of polymeric subcoats on the drug release properties of tablets powder-coated with pre-plasticized Eudragit® L 100-55

The aim of the study was to investigate the properties of sodium valproate tablets that were dry powder-coated with pre-plasticized Eudragit® L 100-55. Polyethylene glycol 3350 (PEG 3350) was used as primer to facilitate initial coating powder adhesion. Solubility parameters were employed to determine the wetting properties of the PEG 3350 primer. Additional PEG 3350 within the powder coating formulation was required to enable powder adhesion to the tablet cores. The application of a subcoat of either Eudragit® E PO or Eudragit® RL PO facilitated adhesion of the enteric polymer to the tablet cores and reduced the amount PEG 3350 required in the coating formulation. Since reduction of the PEG 3350 content produced less water-vapor permeable films, the enteric coating level necessary to control the drug release was decreased. PEG 3350 and Methocel® K4M were incorporated in both Eudragit® E PO and Eudragit® RL PO subcoating formulations as pore forming agents. The influence of the pore forming excipients on physicochemical properties of free powder-cast films was investigated. The miscibility of the PEG 3350 and Methocel® K4M in the film coating was correlated with their ability to function as pore forming agent.