Evaluation of enteric film permeability: Tablet swelling method and capillary rise method

Abstract

Cellulose Acetate Phthalate, CAP, is a common enteric coating polymer and when deposited from an ammoniated aqueous system, the films appear to be water permeable. Permeability is often studied using diffusion cells; however, the characteristics of the sample test film (cast or sprayed) have always been a major concern. In this work, two novel methods, the tablet swelling method and the capillary rise method, have been developed and evaluated using two aqueous CAP systems. For the tablet swelling method, TSM, two parameters have been identified; the rate of thickness increase (RThick) and the maximum thickness (MThick). For the capillary rise method, CRM, two parameters have also been identified; the lag time (LTime) and the rate of rise (RRise) in the capillary tube. CRM can be modified to permit the calculation of water flux across the enteric film. The addition of stearyl alcohol to an aqueous ammoniated CAP system results in a reduction in RThick, MThick and RRise and an increase in LTime, which are all indicative of a reduction in film permeability.