Ionic liquid based microemulsion with pharmaceutically accepted components: Formulation and potential applications

In this paper, we report a novel ionic liquid-in-oil (IL/o) microemulsion which is able to dissolve pharmaceuticals that are insoluble or sparingly soluble in water and most of pharmaceutical grade organic liquids. Towards this approach, the nanometer-sized ionic liquid droplets in isopropyl myristate (IPM) were formed with a blend of nonionic surfactants, polyoxyethylene sorbitan monooleate (Tween-80), and sorbitan laurate (Span-20). A set of ionic liquids (ILs) was tested as a dispersed phase, and it was observed that ILs possessing coordinating anions which are strong hydrogen bond acceptor were most effective in forming microemulsion droplets. The possible formation mechanism was also studied. Ternary phase behavior study clearly indicated the formation of optically transparent and thermodynamically stable microemulsions with a wide range of IL content. The shape, size and size distribution of the aggregates in microemulsions were characterized using dynamic light scattering (DLS), which demonstrated the formation of spherical micelles in the range of 8-34 nm. In order to explore the use of newly developed microemulsion as a potential drug carrier, we have investigated the solubility of some drug molecules (e.g., acyclovir, methotrexate and 1-[(5-(p-nitrophenyl) furfurylidene) amino] hydantoin sodium) that are insoluble or sparingly soluble in most of the conventional solvents. Very significantly, the solubility studies indicated a high degree of solubilization of such drugs in IL microemulsions. We believe that this microemulsion formed with ILs having the unique physical, chemical and biological properties may offer novel opportunities to develop a potential drug delivery carrier for poorly soluble drugs molecules.