Hydrophilic Ionic Liquids as Ingredients of Gel-Based Dermal Formulations

Ionic liquids (ILs) have several properties that offer many advantages in dermal drug delivery systems. Depending on the chemical structure, ILs can be used for protection against microorganisms, to enhance skin penetration, and as a solvent. In the present work, SEPINEO™ P 600 formulations and hydroxyethylcellulose gels containing the hydrophilic ILs hexylpyridinium chloride, choline dihydrogen phosphate, and 1-ethyl-3-methylimidazolium ethyl sulfate were prepared, and the influence of the ILs on the formulation properties was evaluated. ILs were successfully incorporated into the emulsion structure, resulting in stable formulations. The antimicrobial activity of the ILs was estimated. The minimal inhibitory concentration values for hexylpyridinium chloride are about 2.5 mg/mL. The other two ILs have no antimicrobial activity. Skin penetration enhancement of caffeine, a hydrophilic model substance, was observed in the presence of hexylpyridinium chloride.