Stereochemical aspects of pharmacotherapy.

Over the past 15 years stereoselectivity has become a well-recognized consideration in clinical pharmacology. Drugs that have an asymmetric center or plane of symmetry within their molecular structure are said to be chiral. They are available as pairs of nonsuperimposable mirror images, called enantiomers, that share essentially the same physicochemical properties. These three-dimensional structural differences, however, can translate into enantiospecific pharmacologic or pharmacokinetic properties, which may be important in understanding the clinical pharmacology of chiral drugs. Most chiral drugs are available as the racemate, in which equal proportions of the two enantiomers are administered concurrently. The pharmacologic and disposition properties of many chiral drugs are documented to be stereospecific, and this has influenced the regulatory requirements for the approval of new drug candidates. Due to this influence on new drug development, the possible issues surrounding racemic drugs will undoubtedly affect the types of pharmaceuticals that are used clinically in the next century. Accordingly, considerable advances have been made in producing optically pure drug. It should be emphasized, however, that stereochemically pure drugs are not necessarily superior to the respective racemates.