Enhancement of skin permeation of bufalin by limonene via reservoir type transdermal patch: Formulation design and biopharmaceutical evaluation

A reservoir-type transdermal delivery system (TDS) of bufalin was designed and evaluated for various formulation variables like different penetration enhancers, formulation matrix, rate controlling membranes as well as biopharmaceutical characteristics. Hairless mouse skin was used in permeation experiments with Franz diffusion cells. In vitro skin permeation study showed that terpenes, especially d-limonene was the most effective enhancer when ethanol and PG were used as the vehicle with a synergistic effect. Among different rate controlling membranes, ethylene vinyl acetate (EVA) membrane containing 19% vinyl acetate demonstrated a more suitable release rate for bufalin than the other membranes. In vivo pharmacokinetic study of the bufalin patch in rat showed steady-state of bufalin from 3 h to 12 h. In vivo release rate and cumulative amount analyzed by deconvolution method demonstrated the sustained release of bufalin as long as the patch remained on the animal for at least 12 h. The MRT increased from 1 h of IV administration to 9 h of transdermal administration. In vitro permeation across mouse skin was found to have biphasic correlation with plasma AUC in the in vivo pharmacokinetic study. Current in vitro–in vivo correlation (IVIVC) enabled the prediction of pharmacokinetic profile of bufalin from in vitro permeation results. In conclusion, current reservoir transdermal patch containing 10% d-limonene as a permeation enhancer, 40% ethanol, 30% PG and 15% carbopol–water gel complex provided an improved sustained release of bufalin through transdermal administration. The bufalin patch was successfully applied to biopharmaceutical study in rats and demonstrated the feasibility of this transdermal formulation for future development and clinical trials.