This is a randomized (the study drug is assigned by chance), double blind (neither physician nor patient knows the treatment that the patient receives), parallel group (each group of patients will be treated at the same time), placebo-controlled (an inactive substance is compared with a drug to test whether the drug has a real effect in a clinical trial) multicenter study. The study consists of 4 phases: a Screening Phase (up to 3 weeks); a 17-week flexible dose open-label Transition Phase (open-label phase means that all people know the identity of the intervention); a 12-week fixed dose open-label Maintenance Phase; and a randomized, double-blind, fixed dose, placebo-controlled relapse prevention phase (referred to as the Double-blind Phase). Patients who meet specific stabilization criteria will enter the Double-blind Phase at Week 29. Patients will be randomly assigned, in a 1:1 ratio, to receive either a fixed dose of PP3M or placebo. The Double-blind Phase will be of variable duration; patients will remain in the study until they experience a relapse event or meet discontinuation criteria.