Editing Enantiomer (section)

== Chiral drugs ==
{{Main articles|Chiral drugs|Enantiopure drug}}
'''Enantiopure compounds''' consist of only one of the two enantiomers.  Enantiopurity is of practical importance since such compositions have improved therapeutic efficacy.<ref>{{Cite journal |last=Ariëns |first=Everardus J. |date=1986 |title=Stereochemistry: A source of problems in medicinal chemistry |url=http://dx.doi.org/10.1002/med.2610060404 |journal=Medicinal Research Reviews |volume=6 |issue=4 |pages=451–466 |doi=10.1002/med.2610060404 |issn=0198-6325 |pmid=3534485 |s2cid=36115871}}</ref> The switch from a racemic drug to an [[enantiopure drug]] is called a [[chiral switch]]. In many cases, the enantiomers have distinct effects. One case is that of Propoxyphene. The enantiomeric pair of propoxyphene is separately sold by Eli Lilly and company. One of the partners is [[dextropropoxyphene]], an [[analgesic]] agent (Darvon) and the other is called [[levopropoxyphene]], an effective [[antitussive]] (Novrad).<ref>{{Cite journal |last=Drayer |first=Dennis E |date=1986 |title=Pharmacodynamic and pharmacokinetic differences between drug enantiomers in humans: An overview |url=http://dx.doi.org/10.1038/clpt.1986.150 |journal=Clinical Pharmacology and Therapeutics |volume=40 |issue=2 |pages=125–133 |doi=10.1038/clpt.1986.150 |issn=0009-9236 |pmid=3731675 |s2cid=33537650}}</ref><ref>{{Cite book |last=Ariens |first=E.J |title=Chiral Separations by HPLC |publisher=Ellis Horwwod |year=1989 |location=Chichester |pages=31–68}}</ref>  It is interesting to note that the trade names of the drugs, DARVON and NOVRAD, also reflect the chemical mirror-image relationship.  In other cases, there may be no clinical benefit to the patient. In some jurisdictions, single-enantiomer drugs are separately patentable from the racemic mixture.<ref>{{cite web |title=European Medicines Agency - - Sepracor Pharmaceuticals Ltd withdraws its marketing authorisation application for Lunivia (eszopiclone) |url=http://www.ema.europa.eu/ema/index.jsp?curl=pages/news_and_events/news/2009/11/news_detail_000083.jsp&jsenabled=true |website=www.ema.europa.eu |date=17 September 2018 |access-date=14 February 2011 |archive-date=1 December 2017 |archive-url=https://web.archive.org/web/20171201043407/http://www.ema.europa.eu/ema/index.jsp?curl=pages%2Fnews_and_events%2Fnews%2F2009%2F11%2Fnews_detail_000083.jsp&jsenabled=true |url-status=dead }}</ref> It is possible that only one of the enantiomers is active. Or, it may be that both are active, in which case separating the mixture has no objective benefits, but extends the drug's patentability.<ref>{{cite book |author=Merrill Goozner |url=https://archive.org/details/800millionpilltr00gooz |title=The $800 Million Pill: The Truth Behind the Cost of New Drugs |publisher=University of California Press |year=2004 |isbn=0-520-23945-8 |format=excerpt}}</ref>