Effect of Tocopheryl Polyethylene Glycol Succinate on the Percutaneous Penetration of Minoxidil from Water/Ethanol/Polyethylene Glycol 400 Solutions

In a study from 2006, researchers investigated the impact of tocopheryl polyethylene glycol succinate (TPGS) on the skin penetration and retention of minoxidil from topical solutions. The study involved ten different solvent formulations containing varying ratios of water, alcohol, and polyethylene glycol 400 (PEG 400). The results indicated that TPGS improved minoxidil solubility primarily in formulations with higher water and PEG 400 content, particularly at concentrations above 5%. In contrast, formulations with a higher alcohol content showed little change in minoxidil solubility with added TPGS, and sometimes even a decrease in solubility with higher TPGS amounts. The addition of TPGS also increased the penetration flux of minoxidil in formulations with lower solubility parameters, while decreasing it in those with higher solubility parameters. The optimal formulation for enhanced local effect and reduced systemic absorption was found to be F6, which had an alcohol to PEG 400 ratio of 50:50, outperforming the reference product, 2% Regaine®. TPGS was found to be retained mostly in the stratum corneum of the skin, with retention amounts proportional to the TPGS levels in the formulations.