A total of 885 patients will be included in this clinical trial, which will last for approximately 12 months, including screening, treatment and medication-free follow-up period as well as final reporting. The duration for the individual patient is approximately 22 weeks (Visit 1 - Visit 7). After a 2-week screening phase, treatment will be started by application of either 240 mg or 480 mg daily dose (t.i.d.) or placebo for 12 weeks followed by a medication-free follow-up period.