Multifunctional Ionic Liquid Drugs

Formulating drugs as room-temperature liquid salts offers a new approach to circumventing low solubility, bitter taste, and other problems associated with tablet forms of common drugs. In the latest development in this endeavor, Katharina Bica of Queen’s University Belfast and Robin D. Rogers of Queen’s University Belfast and the University of Alabama, Tuscaloosa, discovered that formation of oligomeric anions of pharmaceutically active compounds are key to expanding the liquid ranges of drugs (Chem. Commun. 2010, 46, 1215). The researchers reacted solid salicylic acid with solid tetrabutylphosphonium salicylate. Salicylic acid is an analgesic and antiseptic ingredient widely used in skin care products. The salicylic acid and salicylate anion hydrogen bond to form an oligomeric anion complex that drives down the melting point of the salt (shown) below room temperature. Rogers’ group expanded the concept to dual functional liquid salts by coupling salicylate or acetylsalicylate (aspirin) with cations of antibacterials, local anesthetics, and other drugs (Phys. Chem. Chem. Phys. 2010, 12, 2011). “Although an ionic liquid strategy should be considered as another tool in drug development, design, and delivery, such an approach may not be applicable in every instance,” the researchers caution.