Great expectations in stereochemistry: focus on antidepressants

Chirality has become an increasingly important consideration in the development of psychoactive drugs because enantiomers often show major differences in their pharmacokinetic and pharmacologic properties. This review illustrates the implications of stereochemistry in clinical psychopharmacology using the antidepressant class of drugs as a focus. In many cases, a better understanding of stereochemistry can improve therapeutic outcomes. For example, with citalopram, the racemic formulation is effective for depression as well as panic and obsessive-compulsive disorders. However, the S-enantiomer, escitalopram, is at least twice as potent as racemic citalopram as an inhibitor of serotonin reuptake, implying that it can be used at lower doses, while offering an improved therapeutic index as well as an improved safety profile and reduced drug interaction liability. Clinical trial data support these advantages. Continuing research on the stereochemical properties of psychoactive drugs should simplify the characterization of dose-response relationships, and clarify the effects of disease states, genetic polymorphisms, pregnancy, age, and gender on stereoselective pharmacokinetics and pharmacodynamics. Better understanding of the fate of chiral psychotropic agents and the factors that influence their stereoselective disposition and actions will provide a rational basis for their expanded use in various patient populations.