LIQUID TRANSPORT CONTROLLED RELEASE PROCESSES IN POLYMERIC MATERIALS - APPLICATIONS TO ORAL DOSAGE FORMS

Polymers are being more widely used in many various applications, especially in pharmacy for the preparation of oral dosage forms, with controlled release of the drug. The drug is dispersed in the polymer which plays the role of a matrix, and one or two polymers can be used for the same dosage form, each polymer conferring a particular property. The process of release of the drug is rather complex. The gastric (or intestinal) liquid enters the polymer, dissolves the drug, and thus enables the drug to leave the dosage form through the liquid located in the polymer. These two matter transfers (liquid, drug) are controlled by transient diffusion. Moreover, the diffusivity of the drug is generally expressed in terms of the concentration of the liquid in the polymer. No mathematical treatment is effective, and numerical methods based on finite differences must be used to resolve the problem. Such numerical methods must take into account all the known facts. Generally, they are very efficient, and are able not only to predict the kinetics of release of the drug but also to determine the concentration profiles of both the liquid and the drug in the dosage form.