Although release profiles of drug from hydrophilic matrices have been well recognized, the visual distribution
of hydroxypropylmethylcellulose (HPMC) and atoms inside of internal structures of hydrophilic HPMC matrices has not
been characterized. In this paper, drug release mechanism from HPMC matrix tablet was investigated based on the release
behaviors of HPMC, physical properties of gelled HPMC tablet and atomic distributions of formulation components using
diverse instruments. A matrix tablet consisting of hydroxypropyl methylcellulose (HPMC 6, 4,000 and 100,000 mPa·s),
chlorpheniramine maleate (CPM) as a model and fumed silicon dioxide (Aerosil® 200) was prepared via direct compression.
The distribution of atoms and HPMC imaging were characterized using scanning electron microscope (SEM)/
energy-dispersive X-ray spectroscopy (EDX), and near-infrared (NIR) analysis, respectively as a function of time. A texture
analyzer was also used to characterize the thickness and maintenance of gel layer of HPMC matrix tablet. The HPMC
matrix tablets showed Higuchi release kinetics with no lag time against the square root of time. High viscosity grades of
HPMC gave retarded release rate because of the greater swelling and gel thickness as characterized by texture analyzer.
According to the NIR imaging, low-viscosity-grade HPMC (6 mPa·s) quickly leached out onto the surface of the tablet,
while the high-viscosity-grade HPMC (4000 mPa·s) formed much thicker gel layer around the tablet and maintained
longer via slow erosion, resulting in retarded drug release. The atomic distribution of the drug (chlorine, carbon, oxygen),
HPMC (carbon, oxygen) and silicon dioxide (silica, oxygen) and NIR imaging of HPMC corresponded with the dissolution
behaviors of drug as a function of time. The use of imaging and texture analyses could be applicable to explain the release-
modulating mechanism of hydrophilic HPMC matrix tablets.