In this study we will assess the effect of Ketamine infusion on depressive symptoms and in particular its effect on Suicidal behavior, ideation and thoughts in patients with treatment- resistant MDD.

A Twice repetition of IV infusion of 0.5 mg/kg of ketamine produces an antidepressant response in individuals with treatment-resistant MDD

The work aims to:

1. To assess the onset of action and degree of improvement and the duration of antidepressant effect of ketamine in a sample of patients with treatment -resistant major depressive disorder.
2. To find out whether the onset of Ketamine antidepressant effect is associated with an improvement of suicidality in those patients.

Inclusion Criteria:

1. Patients fulfilling diagnostic criteria of treatment-resistant MDD.
2. Presence of suicidal risk.
3. No comorbid medical or neurological conditions.
4. Age above 18 years old.
5. Both gender.
6. Informed written consent from the patient or his legitimate.

Exclusion Criteria:

1. Presence of perceptual disturbance.
2. History of sensitivity to ketamine.
3. Refusal to participate in the study.

The Sequentially Numbered, Opaque, Sealed Envelope technique (Schulz and Grimes, 2002) was employed: the randomization group was listed on paper and preserved in an opaque sealed envelope with a serial number. When a patient agreed to participate, the pharmacy (care provider) opened the sealed envelope and assigned the patient to the appropriate treatment group on the morning of their first infusion.