Importance of drug enantiomers in clinical pharmacology.

The ordered asymmetry of biological macromolecules allows them to differentiate between the optical isomers of monomeric substrates. Optical isomers of drugs often have greatly different affinities at receptor sites, are metabolised at different rates, and have different affinities for tissue and protein binding sites. Despite this knowledge, many drugs are administered as their racemates. Manipulation of the enantiomeric ratio or the use of only one enantiomer of a drug may allow separation of toxicity and efficacy, and this may lead to a significant increase in therapeutic ratio and a more rational approach to therapeutics.