Drug chirality and its clinical significance

Approximately 1 in 4 therapeutic agents are marked as racemic mixtures, the individual enantiomers of which frequently differ in both their pharmacodynamic and pharmacokinetic profiles. The use of racemates has become the subject of considerable discussion in recent years, and an area of concern for both the pharmaceutical industry and regulatory authorities. The use of single enantiomers has a number of potential clinical advantages, including an improved therapeutic/pharmacological profile, a reduction in complex drug interactions, and simplified pharmacokinetics. In a number of instances stereochemical considerations have contributed to an understanding of the observed pharmacological effects of a drug administered as a racemate. However, relatively little is known of the influence of patient factors (e.g. disease state, age, gender and genetics) on drug enantiomer disposition and action in man. Examples may also be cited where the use of a single enantiomers, nonracemic mixtures and racemates of currently used agents may offer clinical advantages. The issues associated with drug chirality are complex and depend upon the relative merits of the individual agent. In the future it is likely that a number of existing racemates will be re-marketed as single enantiomer products with potentially improved clinical profiles and possible novel therapeutic indications.