Experimental determination of the theophylline diffusion coefficient in swollen sodium-alginate membranes

In this paper attention is focused on the determination of the drug diffusi on coefficient in a swollen polymeric membrane referring to a recent mathem atical model (linear model). The main advantage deriving from its use is th at, despite its analytical nature and its ability to account for the most i mportant aspects characterising a permeation experiment, it can also be app lied in the case of thick membranes. To check the model reliability, a comp arison is made with a more complex numerical model and with a largely emplo yed model in terms of data fitting quality. To this purpose, particular car e is devoted to the experimental and theoretical tools employed to calculat e the auxiliary parameters required by the three models, and with the aim o f getting a drug diffusion coefficient value as accurate as possible. Theop hylline was chosen as model drug owing to its wide employment in the pharma ceutical field. Membranes were prepared with sodium alginates hydrogels at three different polymer concentrations. The present analysis demonstrates t he reliability of the linear model and reveals that the theophylline diffus ion coefficient is not significantly affected by the polymer concentration. Indeed, such a parameter is reflected in different membrane thicknesses ra ther than in different mesh sizes of the polymeric network. (C) 2001 Elsevi er Science B.V. All rights reserved.