Patients will undergo two weeks of prospective observation, they will then receive ketamine IV 0.5mg/kg over 45 minutes as augmentation of their ongoing antidepressant regimen; after three infusions this dose will be increased increase to 0.75 mg/kg in non-responders. The schedule of administration will be twice a week for 3 weeks. After this phase, the patient will be followed with assessments every two weeks for three months.
Total duration of the study is 5 months.
