Teriflunomide is the primary metabolite of leflunomide, which is marketed worldwide for the treatment of rheumatoid arthritis. Teriflunomide inhibits dihydroorotate dehydrogenase( DHODH), the forth enzyme in the de novo synthesis pathway of pyrimidines.Activated T-lymphocytes utilize both the de novo pyrimidine and salvage pathways of pyrimidines ribonucleotide synthesis.After mitogen stimulation, teriflunomide inhibits in vitro T cell proliferation, DNA and RNA synthesis and expression of cell surface and nuclear antigens that are directly involved in T-cell activation and proliferation.