Study of NMDA Antagonists and Neuropathic Pain

Inclusion Criteria:

• > 18 years old

• patient suffering chronic neuropathic pain

• All chronic pain is retained except central or diabetic pain

• Answering patient at ketamine in pain treatment by investigator, and having alreadyreceived ketamine

• Patient who completed before ketamine the following evaluation : DN4, QCD, QDSA, PGIC questionnaires, HAD scale, Leed's sleep evaluation and SF36.

• Patient who completed at the end of treatment the following evaluation : numericalscale and PGIC

• Sufficient cooperation and understanding to comply to the requirements of study

• Acceptance to give a written concert

• Affiliation at system of French social security

• Inscription or acceptation of inscription at national register of voluntariesparticipant at research

Exclusion Criteria:

• Against-indication at memantine or dextromethorphan administration : hypersensitivityat active substance or excipients, hypertension, antecedent cerebrovascular accident,severe cardiac insufficiency

• Patient with medical or surgical antecedents

• Patient with progressive disease at balance of inclusion

• Patient treated by an IMAO

• Woman in childbearing age not using effective contraceptive method, pregnant orlactating woman

• Patient who participated in another clinical trial, located in exclusion period orreceived benefits > 4500 euros during 12 months before the beginning of trial

• Patient with cooperation and understanding insufficiency to comply to the requirementsof protocol

• Patient with social protection

• No affiliation at system of French social security