Ketamine and Neuropathic Pain

Inclusion Criteria:

* Patient (s) are at least18 years old, with chronic pain (for more than 3 months), having the characteristics of a peripheral or central neuropathy, follow (s) at the Pain Clinic CHU Clermont-Ferrand and justifying the establishment of a therapeutic program including intravenous infusion of ketamine (as therapeutic test);
* Patient (s) who had never received ketamine infusion under the care of their neuropathic pain;
* History of illness compatible with an injury or disease of the somatosensory system;
* Localized pain in an anatomical neuro territory;
* Neurological examination shows sensory abnormalities,
* The patients of childbearing potential must use effective contraception throughout the study;
* For womens of childbearing age, they will be enrolled in the study after a negative urine pregnancy test; in case of suspicion of pregnancy, a blood pregnancy test should be performed;
* Cooperation and willing to follow the study;
* Acceptance to give written consent;
* Affiliated to the French social security;
* Inscription or acceptation of inscription in the national register of volunteers involved in trials.

Exclusion Criteria:

* Patient (s) who have received intravenous ketamine infusion;
* Patients with one or many contraindication to ketamine administration: known hypersensitivity to ketamine in which one of the constituents of the product, uncontrolled high blood pressure, severe cardiac insufficiency;
* Patients with one or many contraindication of magnesium sulfate administration: Patients with severe renal impairment;
* Patients with one or many contraindication to administration of sodium chloride: water inflation, fluid retention;
* Patients with a medical history and / or surgical judged by the investigator to be not consistent with the clinical trial;
* Patients with drug treatments judged by the investigator to be not consistent with the clinical trial;
* Pregnancy or lactation women;
* Patient who participated in another clinical trial, located in exclusion period or received benefits \> 4500 euros during 12 months before the beginning of trial;
* Patients with cooperation and understanding not to adhere strictly to the conditions provided in the clinical trial;
* Patients receiving a measure of legal protection (guardianship…);
* Patients are not affiliated to the System of the French Social Security