Exploiting the Power of Stereochemistry in Drugs: An Overview of Racemic and Enantiopure Drugs

Stereochemistry is one of the essential dimensions in pharmacology as it dictates how enantiomers interact with biological systems. Chirality is very important in drug design. Enantiomers of the same chiral drug can have different pharmacodynamic and/or pharmacokinetic properties. In this context, replacing some existing racemates with single isomers has resulted in improved safety and/or efficacy profile of various racemates. Single enantiomer drug use can potentially lead to simpler and more selective pharmacologic profiles, improved therapeutic indices, simpler pharmacokinetics due to different rates of metabolism of the different enantiomers, decreased drug interactions, and drug companies are increasingly using chiral switching as a marketing strategy. Additionally, due to different pharmacological activity, enantiomers of chiral drugs can differ in toxicity. However, unpredicted toxicity has been reported in some chiral switching cases which has resulted the withdrawal of the enantiomer from the market or a halt in its development. In view of above, before switching to single enantiomer drugs, prescribers should look for evidence from well-conducted clinical trials to prove that the chiral switch is cost-effective and improves the outcomes for patients rather than patents. The U.S. Food and Drug Administration (FDA) have allowed single enantiomers of generic drugs to be patented and marketed under different name. FDA regulations require that all chiral bioactive drug molecules must be isolated and tested for the efficacy and safety, and have to be as pure as possible containing a single pure enantiomer.