A NOVEL NUCLEAR-MAGNETIC-RESONANCE (NMR) IMAGING METHOD FOR MEASURINGTHE WATER FRONT PENETRATION RATE IN HYDROPHILIC POLYMER MATRIX CAPSULE PLUGS AND ITS ROLE IN DRUG-RELEASE

An NMR imaging method was developed to estimate the rate of water move ment in slow-release capsule matrices of pseudoephedrine HCl and hydro xypropyl cellulose (HPC). Test capsules were first placed in a USP met hod 2 (paddles, 50 rpm) dissolution apparatus. Each plug was removed f rom the dissolution medium at predetermined times, blotted dry, and pl aced within the magnetic field of a General Electric 400-MHz wide-bore NMR spectrometer equipped with a microimaging accessory. Images were recorded along the transverse plane of each plug. The water penetratio n rate was determined by comparison of the cut and weighed contour plo ts of the images acquired. After 1 hr, the plugs tamped to 200 N exhib ited water penetration to the center, while only 45% of the drug was r eleased. The percentage dry matrix was fitted to the Jest equation to obtain a diffusion coefficient of 4.15 x 10(-6) cm(2)/sec. NMR imaging is set forth as an important and practicable technique to investigate drug formulations. In the HPC matrix system of this study, the NMR im aging results convincingly revealed the rate of hydration front penetr ation not to be a rate-limiting step in the drug release process.