Stability of aqueous polymeric controlled release film coatings

Aqueous polymeric film coatings provide a great potential to accurately control the release rate of a drug from a pharmaceutical dosage form, while avoiding the various disadvantages associated with the use of organic solvents. However, long term instability of drug release, due to imperfect film formation during coating and curing, can be a serious concern. If the coalescence of the particles continues during storage, the film permeability can decrease, slowing down drug release. Different strategies can be used to effectively avoid this phenomenon, including optimized curing conditions, the addition of appropriate additives and the use of specific packaging materials. This article gives an overview on the current state of the art in this field. Various practical examples are described, covering different types of polymer coatings and drugs. The aims are: (i) to provide a better understanding of the release patterns and potential changes thereof, and (ii) to help identifying strategies allowing for improved long term stability for specific types of polymer coatings.