The study duration is a maximum of approximately 14 weeks including up to 2 weeks for screening, up to 2 weeks for proper dose finding, followed by an 8 week treatment period and a follow-up visit after 2 weeks. A sufficient number of patients will be screened to allow approximately 211 randomized patients. An extension study is also available to continue treatment if determined appropriate by the study doctor. This Study is NCT01132326 sponsored by Chelsea Therapeutics and is enrolling by invitation only.