Estimate the Efficiency of the Association of an Injection of Ketamine and the Venlafaxine in the Severe Major Depressive Disorder for Six Weeks

Inclusion Criteria:

* Patients aged 18 or over,
* Introducing a single depressive episode or recurrent unipolar
* Responding to the diagnosis of severe major depressive episode according to DSM IV (Diagnostic and Statistical Manual of Mental Disorders - Fourth Edition): MADRS score ≥ 20,
* absence of treatment with ketamine for analgesia or anesthesia during the last 6 months
* Affiliate (or beneficiary) to a social security system
* Informed consent signed

Exclusion Criteria:

* Contraindication to ketamine administration or treatment with venlafaxine;
* Failure of treatment with venlafaxine in the current episode (as low as 150 mg for 15 days);
* Axis I diagnosis according to DSM IV bipolar disorder (type I, II or III), schizoaffective disorder, schizophrenia, alcohol and other toxic or weaned for at least 6 months;
* Current Episode resistant stage V according to the classification of Thase and Rush (failed a course of bilateral ECT);
* Major depressive episode with severity criteria (significant risk of suicide is a MADRS score ≥ 5-SI; decubitus complications, intravenous hydration);
* episode currently being treated with fluoxetine;
* Patients hospitalized without their consent or measure of legal protection (guardianship, curatorship);
* Affection Organic likely to affect cognitive abilities and brain structures (eg, HIV, MS, lupus, Parkinson's disease, epilepsy, dementia ...) or decompensation;
* Pregnancy or breastfeeding underway.