Prospective, multicenter, double-blind, phase II, randomized, dose-response study in 5 parallel groups (dose-range).

Obstructive sleep apnea (OSA) is a relatively common condition and is estimated to affect 2 to 4% of middle-aged adults

The study medication BF2.649 tested here is a novel, highly potent, selective, orally active inverse agonist at the histamine H3 receptor, therefore strengthens histaminergic transmission in the brain and increases wakefulness EDS is characterized by daytime somnolence and sudden sleep episodes. This problem has several consequences, e.g., an impairment of quality of life, an interference with activities of daily living and other handicaps in the management of social and family affairs.

The primary endpoint of this study will be measured by the change in the well-validated Epworth sleepiness scale (ESS). The ESS is a simple self-administered 8-item questionnaire. The outcome is to get an impression about the level of the daytime sleepiness in several real-life situations.

In this study, each patient will be treated during 2 weeks, and randomly assigned to one the 5 arms (BF2.649 at one of the 4 possible dosages or placebo).

The patient will then attend a end-of-treatment visit, in order to assess the particularly the ESS score.

Main inclusion Criteria:

• Patient with OSA (treated or not with nCPAP) and still complaining of EDS
• Epworth Sleepiness Scale score > or = to 11

Main exclusion Criteria:

• Patient suffering from chronic severe insomnia in accordance with the International Classification of Sleep Disorders, but without OSA