Vestipitant 28-day Tolerance Study

Inclusion Criteria: * Male and female aged 18-64 years inclusively with Diagnosis of Primary Insomnia according to Diagnostic and Statistical Manual of Mental Disorders -Text Revision (DSM-IV-TR) criteria 307.42 * PSG variables collected during 2consecutive PSG screening nights falling as follows: TST between 240-420 mins inclusive (both nights) - LPS (Latency to Persistent Sleep): mean not less than 20mins, each night not less than 15 mins - WASO (Wake After Sleep Onset): mean not less than 60mins, each night not less than 45mins * Women: non child bearing potential or if child bearing potential agree on Contraceptive Methods listed in Protocol Exclusion Criteria: * clinically significant Psychiatric and neurological disorders (sleep disorders other than Primary Insomnia, history of alcohol orother substance abuse or dependnce); * nightshift or rotating shift-work; * Lifestyle habits in agreement with Protocol requirement: caffeine - alcohol intake and smoke * healthy according to GSK criteria - laboratory and ECG limits set in the Protocol