A NOVEL IN-SITU MODEL FOR CONTINUOUS OBSERVATION OF TRANSIENT DRUG CONCENTRATION GRADIENTS ACROSS BUCCAL EPITHELIUM AT THE MICROSCOPIC LEVEL

Buccal drug delivery is hindered by the low permeability of the buccal epithelium. The use of a time- and space-resolved visualization techn ique is inevitable for finding the location of the rate-limiting regio ns in the epithelium. In this study an in-situ method is presented wit h which permeation of fluorescent compounds in and across buccal epith elium can be visualized by means of confocal laser scanning microscopy (CLSM) and their topographical distribution quantified. This direct a pproach to visualize the penetration of fluorescently labelled drugs i n thick epithelia avoids artifacts due to fixation, dehydration and em bedding and can be executed on a single piece of tissue. Using this me thod, i.e. visualizing and quantifying the transepithelial drug distri bution as a function of time, a rate-limiting zone in porcine buccal e pithelium was observed at approximately 150 mu m from the surface, in the epithelium. The region where diffusion of fluorescein isothiocyana te (FITC), a hydrophilic marker, was slowed down corresponds with the intermediate strata, the cell layers where membrane coating granules e xtrude their content in the intercellular space.