Teriflunomide is the active metabolite of leflunomide. Teriflunomide was investigated in the Phase III clinical trial TEMSO as a medication for multiple sclerosis (MS). However, the subsequent TENERE head-to-head comparison trial reported that "although permanent discontinuations [of therapy] were substantially less common among MS patients who received teriflunomide compared with interferon beta-1a, relapses were more common with teriflunomide." Teriflunomide is an immunomodulatory drug inhibiting pyrimidine de novo synthesis by blocking the enzyme dihydroorotate dehydrogenase. It is uncertain whether this explains its effect on MS lesions. Teriflunomide inhibits rapidly dividing cells, including activated T cells, which are thought to drive the disease process in MS. Teriflunomide may decrease the risk of infections compared to chemotherapy-like drugs because of its more-limited effects on the immune system.
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