Teriflunomide concentration in cerebrospinal fluid and serum will be determined in 12 patients with multiple sclerosis. They have been treated for at least 6 months and the sampling from blood and by spinal tap is done before dose at 8 am in 10 patients and at 12 am in 10 patients. The dependence from age, sex, and blood-brain barrier (BBB) integrity will be evaluated.The ratio between serum and cerebrospinal fluid will determine the passage over the BBB.
