Comparison of Ionic Liquids and Chemical Permeation Enhancers for Transdermal Drug Delivery

Abstract Transdermal delivery offers a patient‐friendly method of drug administration. An ideal formulation for transdermal drug delivery should have high potency to enhance skin permeation and low tendency to induce skin irritation. Ionic liquids (ILs) and deep eutectic solvents (DESs) have recently been proposed to serve as an excellent platform to enable transdermal delivery of various therapeutics including proteins and siRNA. In spite of their success, general safety‐efficacy behavior of ILs/DESs is not reported. Using safety and efficacy as two design criteria, a Fourier transform infrared (FTIR) spectroscopy study is conducted to compare the performance of 31 ammonium‐based ILs/DESs and 44 conventional chemical permeation enhancer (CPE) molecules. FTIR analysis of skin stratum corneum exposed to ILs/DESs and CPEs is performed to extract features indicative of their safety and efficacy. ILs/DESs, as a class, outperformed conventional CPEs in terms of both potency and safety. Analysis of ILs/DESs and CPEs based on Hansen solubility parameters indicates that ILs/DESs possess solubility parameters close to those of skin, which may explain their superiority over CPEs. These studies support ILs/DESs as promising materials for novel drug delivery systems.