Stereoisomers and drug toxicity. The value of single stereoisomer therapy.

All drugs produce adverse effects, though the risk varies widely between different compounds. Many toxic reactions are an extension of the mechanism responsible for the therapeutic effect and can be avoided by careful dose adjustment. Other adverse events are not related to the beneficial action of the drug. Recent interest has focused on the role of the different properties of individual drug enantiomers in causing drug toxicity. For drugs with a single chiral centre, both enantiomers may be therapeutically active. However, if the main therapeutic benefit is in only 1 enantiomer, several possibilities exist for the other enantiomer--inactive, a qualitatively different effect, an antagonistic effect or greater toxicity.