Pharmacokinetic parameters obtained with racemates

The extensive therapeutic use of racemates of chiral drugs, wherein one enantiomer contains most, if not all of the biological activity, raises questions about the usefulness of pharmacokinetic parameters based on measurements of racemic drug. Not only do individual enantiomers behave as distinctly different chemicals with respect to their pharmacologic and toxicologic actions but also with respect to their fate in the body. Therefore, it is critically important, as Thomas Walle and U. Kristina Walle point out, to realize that blood concentrations and pharmacokinetics of racemates often do not reflect those of the active enantiomers.