Effects of Ketamine in the Acute Phase of Suicidal Ideation

The primary objective of this study is to assess the efficacy of ketamine versus a placebo for the short-term (at 72h, i.e. 24h after the last perfusion) relief of suicidal ideation, measured using the BSS hetero questionnaire, in patients hospitalized for suicide risk.

The secondary objectives of this study are to assess:

A. The maintenance of medium-term effectiveness of ketamine on the resolution of suicidal ideation

B. The evolution of the full spectrum of suicidality under ketamine compared to placebo

C. The evolution of psychic and physical pain scores under ketamine compared to placebo

D. The evolution of Beck Hopelessness score which is a predictor of long-term suicide risk, under ketamine compared to placebo

E. The early antidepressant efficacy of ketamine in depressed, uni- or bipolar patients

F. The somatic and psychological tolerance of ketamine

G. An overall improvement in the clinical condition of the patient by the practitioner

H. Creation of a biological collection for future ancillary studies dedicated to genetic analysis (microRNA and mRNA).

I. The efficacy of ketamine versus a placebo for the short-term (at 72h, i.e. 24h after the last perfusion) relief of suicidal ideation, measured using the BSS self-report questionnaire, in patients hospitalized for suicide risk.

Eligibility Criteria:
Inclusion Criteria:

* French speaking patients freely hospitalized for prevention of suicide and who have a medium or high suicide risk score according to a MINI structured interview
* The patient is able to understand how the study is carried out and the tests performed
* The patient is deemed capable of giving his/her informed consent
* The patient has been correctly informed
* The patient must have given his/her informed and signed consent.
* The patient must be insured or beneficiary of a health insurance plan.
* Presence of suicidal ideation according to the SSI score (score \> 3)
* Negative pregnancy test for women of childbearing age

Exclusion Criteria:

* The patient is participating in another interventional study
* Within the past three months, the patient has participated in another interventional study
* The patient is in an exclusion period determined by a previous study
* The patient is under judicial protection
* The patient is an adult under guardianship
* The patient refuses to sign the consent
* The patient is not able to understand the informed consent
* Pregnancy or breastfeeding
* History of schizophrenia or other psychotic disorders
* Presence of psychotic symptoms at initial interview
* Schizoid or schizotypic personality disorder
* Positive urine screening for illicit substances, excluding cannabis
* Substance dependence in the preceding month (excluding nicotine or caffeine)
* Concomitant treatment with electroconvulsive therapy
* Unstable somatic pathology
* Clinically significant anomalies found during clinical examination, biological test or ECG
* Non-stabilized hypertension or hypertension \> 180/100
* Known or suspected contra-indication for ketamine (includes interactions): hypersensitivity to ketamine, hypertension, class IV cardiac insufficiency, history of stroke, hepatic or cutaneous porphyria, history of intracranial hypertension