Efficacy and Safety of Eplivanserin 5mg/Day in Insomnia Characterized by Sleep Maintenance Difficulties

Primary objective:

- To assess the efficacy of eplivanserin 5mg/day in comparison to placebo after 6 weeks of treatment on sleep maintenance of insomniac patients, as measured by Polysomnography Wake Time After Sleep Onset (PSG-WASO) and Polysomnography Number of Awakenings (PSG-NAW).

Secondary objectives:

* To evaluate the effects of eplivanserin 5mg/day as compared to placebo after 6 weeks of treatment on other sleep parameters measured by PSG recordings (Total Sleep Time - PSG-TST, Sleep Efficiency - PSG-SE, Latency to Persistent Sleep - PSG-LPS) and reported by patients (Wake Time After Sleep Onset - pr-WASO, Number of Awakenings - pr-NAW, Total Sleep Time - pr-TST, Quality of Sleep - QoS and Refreshing Quality of Sleep - RqoS). * To evaluate the effects of eplivanserin 5mg/day on sleep architecture compared to placebo. * To evaluate the effect of eplivanserin 5mg/day on daytime functioning using the Sleep Impact Scale (SIS), as compared with placebo after 6 weeks of treatment. * To evaluate patient's impression of treatment effects using the Patient's Global Impression questionnaire. * To evaluate the potential for next-day residual effects (using patient's morning questionnaire and psychometric tests) with eplivanserin 5mg/day as compared to placebo. * To evaluate the potential for rebound insomnia following abrupt discontinuation of eplivanserin 5mg/day in comparison with placebo. * To evaluate the effect of eplivanserin, compared to placebo, on the quality of life of patients with primary insomnia using the SF-36 Health Survey. * To evaluate the clinical safety and tolerability of eplivanserin 5mg/day compared to placebo.