History
Zopiclone was first developed and introduced in 1986 by Rhône-Poulenc S.A., now part of Sanofi-Aventis, the main worldwide manufacturer of the drug. Initially it was promoted as being an improvement on benzodiazepines. A recent meta analysis found that zopiclone had no superiority over benzodiazepines in any of the aspects assessed. On April 4, 2005, the U.S. Drug Enforcement Administration listed zopiclone under Schedule IV, due to evidence that the drug has addictive properties similar to benzodiazepines.
Zopiclone, as traditionally sold worldwide, is a racemic mixture of two stereoisomers, only one of which is active. In 2005, the pharmaceutical company Sepracor of Marlborough, Massachusetts began marketing the active stereoisomer eszopiclone under the name Lunesta in the United States. This had the consequence of placing what is a generic drug in most of the world under patent control in the United States. Although it was expected to be available in generic form by 2010, no generic has become available there at present. However, Zopiclone is currently available off-patent in a number of European countries, as well as Brazil, Canada and Hong Kong. The eszopiclone/zopiclone difference is in the dosage—the strongest eszopiclone derivative dosage contains 3 mg of the therapeutic stereoisomer, whereas, the highest zopiclone dosage (7.5 mg) contains 3.75 mg of the active stereoisomer. The two agents have not yet been studied in head-to-head clinical trials to determine the existence of any potential clinical differences (efficacy, side effects, developing dependence on the drug, safety, etc.); the significant possibility that the two drugs have identical effects and only differ in dosing and the simple fact that investing in clinical trials is a very expensive undertaking may be responsible for this line of inquiry thus far remaining unpursued.
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