[Physical ageing of amorphous polymeric excipients III. The possible consequences of ageing]

Polymeric excipients are widely used in pharmaceutical technology, and most of them are amorphous or partly amorphous. A well-known property of such materials is that they undergo physical ageing, which is accompanied by volume and enthalpy relaxation and thus might result in severe structural changes in the polymer. This latter phenomenon can influence the properties of excipients and dosage forms, such as processability, mechanical strength and drug release. These alterations are of great significance in the case of solid dosage forms, as physical ageing occurs in the solid state of the polymer. Considering conventional tablets, the structural changes of fillers or binders along with storage can influence the above mentioned properties, while in the case of modified release tablets, matrix-forming and film-forming agents are to be taken into account, as well. In addition to this, by the examination of films, the presence of plasticizers is of great importance, as these materials can facilitate physical ageing via increasing the molecular mobility of the polymer. In the case of certain therapeutic systems (e.g. intrauterine devices), where the base of the dosage form is polymeric, significant changes are to be noted considering the drug release and physiological tolerability of the system.