Inclusion Criteria:  Age >= 18 years Chronic cluster headache diagnosis made according to ICHD-3 criteria A mean of at least 2 attacks/day during the 14 days before infusion Insufficient efficacy or intolerance or contra-indication to the use of the 3 main validated treatments (verapamil, lithium and sub-occipital steroids injections) Stable preventive treatment for at least 7 days before infusion  Exclusion Criteria:  Pregnant or lactating woman Contra-indication to ketamine use (uncontrolled high blood pressure, stoke history, severe cardiac failure) Ketamine use during the previous year Hypersensitivity to the product or their metabolites Severe renal insufficiency (creatinine clearance < 30ml/min)