Development of a tadalafil transdermal formulation and evaluation of its ability to in vitro transdermal permeate using Strat-M® membrane.

Tadalafil (TDF) has low water solubility, high intestinal permeability and belongs to the Biopharmaceutics Classification System (BCS) Class II. Due to high intestinal permeability, only oral administration (tablets) and oral thin film formulations have been developed. Therefore, it is necessary to develop various formulations, such as external formulations and transdermal absorption formulations requested by patients. The purpose of this study is to improve the solubility and skin permeability of TDF, and to develop a novel transdermal formulation with secured stability over time. The research strategy is to determine solvents that will improve TDF solubility and to screen substances that will enhance TDF permeability. Skin penetration tests were simulated by using a Strat-M® membrane in Franz diffusion cell systems. The optimal formulation (F1, consisting of TDF/HDTMA-Br at a ratio of 1:10 [weight/weight] in DPG) observed the highest permeability compared to all formulations in PBS (pH 7.4). Changes in thermal property of F1 formulation was observed and maintained its stability over 12 months including drug content (μg/mL), appearance, pH, and permeation (μg/cm). In conclusion, DPG played a supported role in improving both TDF solubilization and permeability, whereas HDTMA-Br played a key role in enhancing permeability. It is thought that these results will be supplemented in the future to conduct research and experiments on humans.