Ionic liquids with N-methyl-2-pyrrolidonium cation as an enhancer for topical drug delivery: Synthesis, characterization, and skin-penetration evaluation

Abstract The development of non-toxic ionic liquid-based active pharmaceutical ingredients (IL-APIs) for effective topical drug delivery is still challenging. The properties of IL-APIs can be boosted up by selecting potential biocompatible cations. Here, we introduced N-methyl-2-pyrrolidone (NMP) as a potent biocompatible counter ion to prepare ionic liquefied drugs for topical drug delivery. The cytotoxicity of NMP cation was investigated using mammalian cell lines (HepG2, NIH3T3 and L929 cells) and compared with conventional IL-forming cations. The synthesized NMP cation has lower toxicity than that of conventional IL-forming cations. The NMP cation showed at least 3.6, 15.2 and 58.9 times lower toxicity than that of conventional imidazolium, ammonium and phosphonium cations, respectively. The synthesized NMP-based ionic liquid (NMP-IL) was characterized using 1H & 13C NMR, FT-IR, DSC and TGA. NMP-IL showed better physico-thermal stability, enhanced skin penetration, and enriched drug accumulation 2.6 times higher than that of IL [Cho][Ibu] in the target tissue. These results suggested that NMP cation based API-IL can be an effective biocompatible formulation for topical drug delivery by accumulating active drugs in the skin.