Optical Isomerism and Pharmacokinetic Effects

After administration and before it arrives in the vicinity of its receptor site, a drug is subjected to a variety of physiological processes absorption, distribution metabolism. 

The higher narcotic potency in vivo of the S(+)-isomer of hexobarbital was shown to be related to higher central nervous system (CNS) levels than for the R(-) form, this seems to be due to a better crossing of the blood-brain barrier In a distribution study of [ C] (+) and 

Since all enzymes are chiral in nature, and therefore probably possess some degree of asymmetry at the reactive center, it is not surprising that most metabohc reactions of isomers lead to qualitative and quantitative differences in the metabolites formed. For review articles see Testa, Vermeulen, and Kroemer et 

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IV Optical isomerism and pharmacokinetic effects A Isomer effects on absorption and... 

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