A Study in Patients With Major Depressive Disorder

This is a Phase 2a, placebo-controlled, single-blind study in up to 24 patients with major depressive disorder (MDD). Subjects will sign consent form prior to any study related procedure and will complete screening assessments. Subjects will be randomized to either the treatment group or the placebo group at a ratio of 1:1. The study will be conducted in two parts. Titration period On Day 1, subjects will complete all baseline assessments prior to the 1st dosing. Pramipexole group: Consenting individuals meeting accession criteria will start pramipexole 2.0mg daily dose (1.0mg twice a day) with ondansetron 16mg daily dose (8mg twice a day). Pramipexole will be titrated up daily or every two days depends on each patients' tolerability up to the first intolerable dose (FID) or maximum allowed dose (5 mg/day) according to titration schedule (Table 1). Once subjects reach their FID, their maximum allowed dose (MTD) will be defined as 1 mg below their FID. During titration, subjects will be admitted to the clinic (subjects will be discharged on the day following their pramipexole FID or Day 8 if subjects reach to 5 mg/day of pramipexole. Placebo group will take 3 placebo tablets twice a day. Maintenance period During the maintenance phase, patients will be treated with pramipexole MTD or MAD with ondansetron 16mg/day for the remainder of the 8-week treatment. Placebo group is taking 3 tablets of placebo twice a day during the trial. Exit visit After the Week 8 visit, study medications will be discontinued, and subject will return for Exit visit at Week 9. After the Exit visit, all subjects will return to their prior treatment for depression or started on a new therapeutic regimen as medically appropriate. At study completion (or at other times in accordance with Stopping Rules given below), and all study participants will return to their pre-admission therapeutic regimen or started on a new therapeutic regimen as medically appropriate. Higher doses of pramipexole IR may be tapered off at rates deemed medically appropriate by PI. In this modified single blind study, efficacy raters will be kept unaware of the participants' treatment status. An independent data and safety monitoring board (DSMB) will be appointed to have responsibility for safeguarding the interests of the trial subjects and assessing the safety and tolerability of the study treatments during the trial.