[Stereoisomers in anesthesia. Theoretical basis and clinical significance]

All optically active molecules have at least one asymmetric atom in common which is attached to four ligands, that can have different three dimensional positions. Therefore it can be concluded that the resulting isomers are chemically identical in all respects except for the direction with which they rotate plane-polarized light. When the isomer and its corresponding enantiomer are present in equal proportions, they are called racemic mixture, a mixture that does not rotate polarized light, since the optical activities of the two isomers cancel each other. Although the isomers are chemically identical other optically active molecules can interact with these isomers in a geometrically specific way termed stereoselectivity. The human body comprises a chiral environment due to optically active proteins; thus it is not surprising that enantiomeric drugs exhibit different pharmacological properties, when used as pure optical isomers. Till today most modern anaesthetics have been optical isomers, which are mainly used as racemic mixture (1:1 mixture). For financial reasons pure isomers were only used for research purposes, but nowadays the wide clinical use of pure isomers is financially feasible due to new production techniques. The terms eutomer and distomer were chosen to indicate the more or less potent form of the drug. The clinical use of pure isomers is only of advisable, if there are significant differences between eutomer and distomer in desired or side effects. Among the modern anaesthetics ketamine, isoflurane, bupivacaine and atracurium exhibit an asymmetric carbon. For most drugs the separation in pure isomers will reduce side effects. For volatile anaesthetics this question is still unanswered, since experimental and clinical results are inconsistent so far.