INTRODUCTION
Chirality is an important geometric characteristic of the objects within biological systems including amino acids, carbohydrates, and lipids as well as drugs . In the latter, chirality might be associated with safety issues through pharmacokinetic or pharmacodynamic variations, drug interactions, or direct toxicological responses . Chiral drugs consist of racemic mixtures, non-racemic mixtures, or pure enantiomers . Unlike achiral drugs with no chiral center, this stereoisomeric chemistry allows the opportunity to manipulate their composition or molecular chirality to enhance efficacy and/or overcome tolerability problems . A typical example of improving clinical efficacy could be given as selective H1-receptor antagonist, cetirizine, whose R-enantiomer levocetirizine has 30-fold higher binding affinity and lower renal clearance compared to its parent racemic mixture . On the other hand, thalidomide represents a well-known dramatic example of drug-induced toxicity, with R-enantiomer responsible for the intended sedative effect and S-enantiomer for the tragic phocomelia .
Use of pure enantiomers offers advantages including dose reduction, simplification of dose-response relationship, diminution of interindividual variability and toxicity from inactive enantiomers . In fact, regulatory drug authorities encourage such chemical designations for novel drug development . In addition, some racemic mixtures were undergone chiral switch, where their pure enantiomers were launched with same/similar indication . These have led to increased share of pure enantiomers worldwide though still many racemic and non-racemic mixtures are present . While several clinical efficacy and/or safety benefits have been attributed to pure enantiomer drugs, there has been no systematic analysis that investigated these aspects with respect to chirality. In this study, we aimed to examine chiral status of the drugs withdrawn from the market.