STEREOCHEMISTRY IN ANESTHESIA

1. Interest in the pharmacokinetic and pharmacodynamic properties of t he enantiomers of chiral drugs has greatly increased in recent years. This is particularly so for agents used in anaesthesia. 2. Chiral comp ounds are those that can exist in two non-superimposable forms. Each f orm is termed an enantiomer or stereoisomer. Two naming systems are in use: one uses the terms (+) and (-) to indicate the direction the com pound will rotate polarized light, while the other system, based on th e absolute three-dimensional structure of the enantiomers, uses the te rms R and S. 3. Investigation of the stereoisomers of the volatile ana esthetic agent isoflurane is increasing our understanding of the mecha nism of general anaesthesia. Current evidence suggests a protein, rath er than a lipid, receptor site. 4. Investigation of the stereoisomers of local anaesthetics is increasing the safety of these drugs. 5. For bupivacaine, a widely used amide local anaesthetic, important enantiom eric differences can be found for toxicity, clinical effect and pharma cokinetics. In particular S-(-)-bupivacaine has an improved central ne rvous system and cardiac safety profile. This is partly explained by t he pharmacokinetic differences. 6. Based on these differences, ropivac aine, a propyl homologue of bupivacaine, has been produced solely as t he S-(-)-enantiomer. The available evidence suggests significantly imp roved safety for this agent over racemic bupivacaine.