Structure and dynamics of drug-carrier systems as studied by parelectric spectroscopy.

In the field of topical application without or with little systemic side-effects to reach anti-inflammatory or anti-androgeneous effects, nanoparticles as carriers for drugs as beta-methason-17-valerate, prednicarbate, prednisolone, RU 58841-myristate or cyproterone acetate have proven to enhance the transdermal delivery. This enhancement is closely connected to the interaction of the drug molecules with the lipid carrier systems, i.e. incorporation into the carriers or attachment to their surfaces. Whereas the techniques to measure the penetration profiles in the cutaneous region of the skin are well established in the case of fluorescence microscopy applied to thin slices of epidermis or being established in the case of multiphoton microscopy to monitor this fluorescence, the methods for the investigation of the type of interaction between drugs and carrier systems are relatively new: in the case of electron spin resonance the sample volumes have to be restricted to capillary sizes to avoid parelectric losses in the microwave cavities, in the case of the novel method of parelectric spectroscopy we are free from such restrictions. The application of the latter method will be presented here in detail concerning the underlying theory, the experimental aspects as well as the algorithms to extract the parameters of interest from the measured samples. As samples we restrict ourselves to solid lipid nanoparticles coated with different surfactants as carriers for drug-, dye- or spin label molecules.