Exploring the transmucosal permeability of cyclobenzaprine: A comparative preformulation by standardized and controlled ex vivo and in vitro permeation studies.

As part of early drug development, preformulation studies are used to comprehensively explore the properties of new drugs. In particular, this includes the biopharmaceutical characterization and evaluation of impacting factors (e.g. excipients, microenvironmental conditions etc.) by permeation studies. To overcome the limitations of current studies, a novel standardized ex vivo procedure using esophageal mucosa as surrogate has been established successfully and applied to preformulation studies for oromucosal delivery of cyclobenzaprine hydrochloride, a tricyclic muscle relaxant with potential for psychopharmacotherapeutic use. By using the standardized ex vivo permeation process, a twofold enhancement of permeability (0.98 ± 0.16 to 1.96 ± 0.10 * 10-5 cm/s) was observed by adjustment and controlling of microenvironmental pH, empowering a targeted and effective development of sublingual formulations. Predictivity and suitability were superior compared to in vitro experiments using artificial biomimetic membranes, revealing a determination coefficient (R2) of 0.995 vs. 0.322 concerning pH-dependent permeability of cyclobenzaprine. In addition, diffusion properties were extensively examined (e.g. influence of mucosal thicknesses, tissue freezing etc.). The alignment of the study design regarding physiologically/clinically relevant conditions resulted in ex vivo data that allowed for the estimation of plasma AUC levels in the extend of reported in vivo ranges.