A Study to Evaluate Efficacy and Safety of Zolpidem Modified Release Formulation in Insomnia Patients

Inclusion Criteria: * Diagnosis of primary insomnia based on DSM-IV criteria (307.42) * Written informed consent has been obtained Exclusion Criteria: * Patients with sleep apnea syndrome, narcolepsy, presence or suspicion of periodic leg movement or restless leg syndrome * Patients with hepatic failure, myasthenia gravis, or hypersensitivity to zolpidem * Patients who are known to be current drug or alcohol abuser or likely to concomitantly consume alcoholic beverages (more than 3 times/week) * Patients who are pregnant, lactating or intend to become pregnant during the study period * Patients who have received antidepressants or anxiolytics will not allow to change the dose or discontinue the previous medication throughout the study * Any clinically significant condition, which in the opinion of the investigator makes the patients unsuitable for the trial * Participation in any clinical trial within 1 month prior to randomization