[Chiral switch: towards a better benefit-risk ratio?]

The chirality of drugs has emerged as a major theme in drug design, discovery, development and intellectual property. Single enantiomers offer some advantages and two options are available: the switch from an existing racemic drug to the single enantiomer or the development of an enantiomerically pure chiral drug. At present, the second possibility is systematically considered. The possibility of chiral switch has led to innovative drugs. However, this opportunity may be limited by several factors: the spontaneous interconversion of the two enantiomers, the pharmacokinetic profile or the selective toxicity of the most active enantiomer, and the difficulty of demonstrating the clinical superiority of one enantiomer over the racemate. Finally, the small size of the market, the policies of the drug agencies and/or the patent problem also limit the development of enantiomers. All these factors have led the pharmaceutical industry to develop new galenic forms rather than enantiomers when the patent of the racemate is expiring.