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Single-Enantiomer Drugs

Elegant Science, Disappointing Effects


Most new drugs are marketed as single enantiomers but many older agents are still available in racemic form. As these drugs reach the end of their patent life manufacturers become interested in marketing single enantiomer equivalents. This is called ‘chiral switching’ and it has been claimed that it will bring clinical benefits in terms of improved efficacy, more predictable pharmacokinetics or reduced toxicity. We reviewed the clinical evidence and prices for three recently marketed single enantiomer versions of widely used racemic drugs: escitalopram, esomeprazole and levosalbutamol. Claims of increased efficacy were based on comparisons of non-equivalent doses and any advantages seemed small and clinically unimportant. Prices of esomeprazole and levosalbutamol were higher than their racemic alternatives and we predict that these prices will remain high despite the market presence of generic versions of the racemates. Patent protection and a perception of superiority based on promotion rather than evidence will maintian price premiums for single enantiomer drugs that are not justified on the basis of clinical performance.

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No sources of funding were used to assist in the preparation of this study. The authors have no conflicts of interest that are directly relevant to the content of this study.

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Correspondence to David Henry.

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Mansfield, P., Henry, D. & Tonkin, A. Single-Enantiomer Drugs. Clin Pharmacokinet 43, 287–290 (2004).

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  • Omeprazole
  • Esomeprazole
  • Escitalopram
  • Racemate
  • Patent Protection