Eisai Co., Ltd. and Sepracor Inc. had signed an in-licensing agreement for the insomnia treatment eszopiclone (product name in the US: Lunesta) on July 26, 2007. Under this agreement, Eisai will assume exclusive rights for development and marketing of this compound in Japan.

Eszopiclone is a non-benzodiazepine type allosteric GABA agonist discovered by Sepracor. With its short-acting feature that allows fewer interruptions during sleep, the compound may help patients with transient insomnia as well as chronic insomnia in the elderly.

Furthermore, in clinical studies conducted in the US, the compound was well-tolerated and had a low risk of abuse and dependence even with nightly administration. Currently, a phase I clinical study is ongoing in Japan. In the United States, eszopiclone received approval from the US Food and Drug Administration (FDA) in December, 2004 and has been marketed by Sepracor since April, 2005.

In Japan, it has been reported that more than 24 million people are suffering from sleep disorders and the incidence is expected to increase in the future. With the in-licensing agreement announced, Eisai aims to achieve fast approval of the compound in Japan and to provide further benefits to the patients with insomnia by adding this new treatment to its neurology product portfolio.