SWELLING OF HYDROXYPROPYL METHYLCELLULOSE MATRIX TABLETS .1. CHARACTERIZATION OF SWELLING USING A NOVEL OPTICAL IMAGING METHOD

A novel optical image analysis method was developed to examine the dyn amic swelling behavior of hydroxypropyl methylcellulose (HPMC)-based m atrix tablets in situ. In addition to providing precise determinations of apparent gel layer thickness and the tablet dimension, this method is also capable of estimating the HPMC concentration profile across t he gel layer. The intensity of light scattered from HPMC gels was foun d to depend on polymer concentration. A mathematical model that descri bes the relationship between the scattered light intensity and HPMC co ncentration was derived from Rayleigh scattering theory coupled with t he hypothesis that the turbidity of the gel is an exponential function of polymer concentration. The swelling behavior of a matrix tablet co ntaining 80% HPMC, 17% lactose, and 2.5% adinazolam mesylate is charac terized. The data reveal that as the matrix swells, the polymer concen tration profiles, as well as the gel layer thicknesses, develop equall y in both the axial and radial directions. In addition, the expected d ominant axial expansion of the tablet was also observed. This optical image method is generally applicable to in situ characterization of th e swelling behavior of polymer matrix-based tablets which are commonly used as extended-release dosage forms.