MRI in Pharmaceutical Research

The tablets with controlled drug delivery are one of the promising solutions in pharmacy. The surface of these tablets swells on contact with water. The layer of the hydrogel is formed by polymer hydration and chain relaxation and it has been found that this layer represents a diffusional barrier that retards processes of further water uptake and of drug release. Since the kinetics of drug release must match a proper dosage form, detailed information about dynamics of gel formation is needed. Magnetic resonance imaging (MRI) is a suitable method for this purpose because it is non-invasive and it provides information about the gel layer thickness during the hydration process.

The polymer concentration in a gel layer is not homogenous and a procedure for determining the concentration of polymer in gel was developed. A series of model samples - homogenous gels with known concentration - were prepared. T1 and T2 for each of them were measured at the same temperature and frequency conditions. The theoretical MRI signal was calculated for each of them for the actual imaging parameters, allowing to determine the water concentration for each pixel from the image brightness. In this way we obtained the polymer concentration profile through the whole swelling tablet as a function of time. Better prediction about drug release from hydrated polymer tablets is provided if, in addition to the thickness of a gel layer around the tablet, its hydration structure could be determined.


Changes in polymer concentration as a function of time can be well monitored by MR microscopy.

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