Porcine buccal mucosa as an in vitro model: relative contribution of epithelium and connective tissue as permeability barriers.

Porcine buccal mucosa has been extensively used as an in vitro model to study the permeability of various diffusants and to assess their potential to be delivered through the buccal route. The relative contribution of each component of the buccal mucosa on drug permeability was assessed in this study. The permeability of model diffusants decreased significantly with an increase in the mucosal thickness. A bilayer membrane model was developed to delineate the relative contribution to the barrier function offered by the epithelium and the connective tissue region. The decrease in permeability with mucosal thickness was attributed to the increase in the thickness of connective tissue. However, the epithelium acted as a primary barrier to permeation of all diffusants studied at a mucosal thickness up to 500 microm. In addition, the epithelium exhibited higher resistance to the permeation of hydrophilic diffusants than to lipophilic diffusants. With an increase in buccal mucosal membrane thickness, the lag time for the diffusants increased. Based on the analysis of permeation data, the buccal membrane, as a composite of epithelium and connective tissue, is considered as a heterogeneous permeation barrier. A mucosal tissue thickness of about 500 microm is recommended for in vitro transbuccal permeation studies since the epithelium remained the major permeability barrier for all diffusants at this thickness.