Scientists in the US and Poland have shown that ionic liquids could have significant biological applications in drug delivery.

The unique physical properties of ionic liquids (ILs), such as their low volatility and high stability, have made them a source of fascination for chemists. In recent years, research has moved on to combine the useful physical properties of ILs with precisely targeted chemical properties, for applications such as lubricants and energetic materials.

Robin Rogers at the University of Alabama, Tuscaloosa, US, and colleagues have now taken the application of ILs to a third level, moving on from their physical and chemical attributes to look at their biological properties and applications.

Lidocaine docusate, an ionic liquid based on a common local anaesthetic

Rogers' team made an ionic liquid based on the common local anaesthetic, lidocaine. Lidocaine is usually used in pharmaceutical formulations as the solid hydrochloride salt, lidocaine hydrochloride. But by changing the anion from hydrochloride to docusate (dioctylsulfosuccinate) a room temperature ionic liquid was formed.

Compared to lidocaine hydrochloride, the researchers found that the ionic liquid form of the drug delivered longer lasting pain relief, suggesting that an entirely new but beneficial slow-release mechanism of drug delivery was active.

According to Rogers, the ability to finely adjust the biological properties of ILs by changing their anion/cation combination is a real benefit. 'I am convinced that the tunability inherent to ... ILs is entirely appropriate and applicable to the field of pharmaceuticals,' he said.

Peter Styring, professor of chemical engineering and chemistry at the University of Sheffield, UK, points out that many ILs possess motifs that are also present in drug molecules. 'Much has been asked of the possible toxicology of ILs. This is the first paper [to address] the issue in a positive sense,' he added.

David Parker