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The new trend towards developing enantiospecific drugs has increased the interest in enantiospecific pharmacokinetics of chiral drugs, mainly in the case where only one of the two enantiomers is responsible for the pharmacological activity. Enantiospecific bioassays are also useful in investigating the pharmacokinetic behaviour of the two enantiomers when a given drug is marketed as racemate. The stability of the stereogenic centre in vitro and in vivo, as far as unidirectional and bidirectional inversions are concerned, is another reason for requiring stereospecific assay and bioassay. These assays are often complicated in order to achieve quantification, mainly for in vivo measurements, which are often in the low pg/ml range. This paper considers the enantiospecific bioassays, the methods and approaches used, the need for chemical derivatization, and the difficulties involved. It includes a specific discussion for the genetic polymorphic metabolism involving stereogenic centres., (Copyright 2002 Published by Elsevier Science B.V.)

After administration of pregnenolone-4-C(14) to Holarrhena floribunda leaves, radioactive progesterone was isolated and purified to constant specific activity by chromatography, conversion to a derivative, and recrystallization. The result suggests that the biogenetic sequence leading to progesterone is the same in plants as in animals.