• INCLUSION CRITERIA:

  1. Male or female (not of reproductive potential, unable to conceive) subjects, 18 to 55 years of age. A female patient not of reproductive potential is defined as one who: a) has reached menopause with: i) no menses for the past 3 or more years OR ii) no menses for greater than 1 year but less than 3 years with confirmation of FSH levels elevated into the postmenopausal range; or b) has undergone hysterectomy, bilateral oophorectomy, or bilateral tubal ligation.
  2. Each subject must have a level of understanding sufficient to agree to all required tests and examinations and sign an informed consent document.
  3. Subjects must fulfill DSM-IV criteria for Major Depression (296.3) without psychotic features, based on clinical assessment and confirmed by a structured diagnostic interview, SCID-P.
  4. Subjects must have an initial score of at least 22 on the MADRS at screen and at baseline of study phase II.
  5. Current or past history of lack of response to two adequate antidepressant trials (may be from the same chemical class) operationally defined using the Antidepressant Treatment History Form (ATHF). If subjects have only failed to respond to one adequate antidepressant trial by history, they will be permitted to receive a prospective trial of a standard antidepressant. Subjects who fail to respond to this prospective trial will meet criteria for treatment-resistance and be eligible to randomize. Subjects responding to the prospective trial will be ineligible to randomize. (A CORE representative will be present when the subject is informed as to the decision to randomize or not).
  6. Current major depressive episode of at least 4 weeks duration.

EXCLUSION CRITERIA:

1. Current or past history of bipolar disorder, psychotic features or a diagnosis of Schizophrenia or any other psychotic disorder as defined in the DSM-IV.
2. Subjects with a history of DSM-IV drug or alcohol dependency or abuse (including for nicotine and caffeine) within the preceding 3 months.
3. Subjects with a diagnosis of Obsessive Compulsive Disorder or Posttraumatic Stress Disorder as defined in the DSM-IV.
4. Subjects with a diagnosis of Borderline or Antisocial Personality disorder. Other Axis II disorders do not qualify one for exclusion from the study.
5. Serious, unstable illnesses including hepatic, renal, gastroenterologic, respiratory, cardiovascular (including ischemic heart disease), endocrinologic, neurologic, immunologic, or hematologic disease.
6. Patient has a history of any cardiovascular disease, including myocardial infarction, cardiac arrhythmias or conduction abnormalities, cerebrovascular accident, transient ischemic attack (TIA), or peripheral vascular disease.
7. Patient has systolic blood pressure of less than 90 mm Hg or greater than 135 mm Hg at the screen visit or has orthostatic hypotension at the screen visit (greater than or equal to 20 mm Hg decline in systolic blood pressure compared with previous supine systolic blood pressure plus orthostatic symptoms within 3 minutes after standing).
8. Clinically significant abnormal laboratory test or electrocardiogram.
9. Subjects with uncorrected hypothyroidism or hyperthyroidism.
10. Subjects with one or more seizures without a clear and resolved etiology.
11. Previous lack of antidepressant response to ketamine or hypersensitivity to ketamine or amantadine.
12. Treatment with fluoxetine within 5 weeks prior to study phase I.
13. Treatment with any other concomitant medication not allowed 7 days (14 days for MAOIs) prior to study phase II.
14. Treatment with clozapine or ECT within 2 months prior to study phase II.
15. MADRS greater than 4 on item 10 (suicidal ideation).

No structured psychotherapy will be permitted during the study.