The study will consist of six phases: Prescreening, Screening/Run-in (4 weeks), Treatment Period 1 (4 weeks), Washout (minimum 4 weeks), Treatment Period 2 (4 weeks) and Follow-up (1 week). The total duration of the study for each subject will be at least 17 weeks. There will be up to 6 study visits and a follow-up telephone call.