In this chapter after the definition of traditional microemulsions, a new Chapter 12 type of microemulsion system, namely, ionic liquid based microemulsion, has been introduced. Ionic liquids comprising microemulsions may be acting as polar or nonpolar phases as well as surfactant agent. Then, three types of ionic liquid based microemulsions will be formed as non-aqueous IL microemulsions, aqueous IL microemulsions, and IL/oil/water microemulsions. It has been discussed that the ionic liquid based microemulsions are able to overcome the inabilities of conventional microemulsions to dissolve a number of chemicals which are water insoluble and result in better pharmacological activities of drugs. Most importantly, in the drug delivery field, ionic liquid based microemulsions can serve better bioavailability, permeation, and stability. Additionally, one of the most important applications of ionic liquid based microemulsions, as drug nanocarrier, has been discussed in details. The mechanism of solubility enhancement of an active pharmaceutical ingredient and transdermal drug delivery by using ionic liquid based microemulsion is highlighted. It is also discussed that hydrophobic nontoxic ionic liquids can be used to prepare novel ionic liquid based microemulsions for intravenous administration.
