Most of the drugs reaching the market today are single enantiomers, rather than the racemates that dominated up to ten years ago. Particularly in the field of antibiotics and antifungals the market share of single enantiomers is impressive; more than 80 % of the total market are single enantiomers. Regarding the differential pharmacological profiles of enantiomers and the worldwide regulatory guidelines, it is not surprising that the research activities in the pharmaceutical field are directed towards the development of enantiopure drugs. Nevertheless, the decision to seek approval for a racemate, non-racemic mixture or single stereoisomer depends on a number of factors, including technical feasibility, i.e. production on an industrial scale, stereochemical stability, toxicological profile, the clinical significance of the agent, i.e. risk-benefit ratio, and should be driven be the significance of the pharmacodynamic and pharmacokinetic differences, the clinical importance of the drug as well as marketing advantages. It is evident that due to the high impact of stereoisomerism on metabolism these studies are central to decision making in this area and that the most detailed consideration of the stereochemistry of drug metabolism is justified at every stage through drug development and safety evaluation.

There are no simple answers to the single stereoisomer versus isomeric mixture debate and the demonstrated examples emphasize the importance of considering the impact of stereoisomerism for each compound individually.

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