The strategy of enantiomer patents of drugs.

Enantiomer patents (ENPTs), constituents of chiral switches, claim single enantiomers of chiral drugs previously claimed as racemates. In this article, the strategy of ENPTs and recent court decisions and trends in case law worldwide are highlighted. ENPTs are challenged frequently (e.g. anticipation, obviousness, double patenting and insufficient disclosure), even though the novelty of enantiomers is not destroyed by the description of racemates. For establishing inventiveness (nonobviousness), the description in ENPTs should include superior pharmacological and/or pharmaceutical properties of enantiomer vis-á-vis racemate, above the expected 2:1 ratio. ENPTs were 'obvious-to-try' (unless taught away) since the mid-1980s. General concern about evergreening by ENPTs is not justified. ENPTs should be evaluated on a case-by-case basis. ENPT litigations are especially susceptible to settlements.