About Leflunomide A pyrimidine synthesis inhibitor, Isoxazole derivative, Disease-modifying Antirheumatic Drug. Mechanism of Action of Leflunomide This immunomodulatory drug inhibits dihydroorotate dehydrogenase (an enzyme involved in de novo pyrimidine synthesis) (abbreviation DHODH). It also has anti-inflammatory effect. This double action is slow progression of the disease and to cause remission/relief of symptoms of rheumatoid arthritis and psoriatic arthritis such as joint tenderness and decreased joint and general mobility in human patients. Indications for Leflunomide 1. Rheumatoid arthritis 2. Psoriatic arthritis Interactions for Leflunomide Cholesturamine, charcoal: Co-administration with lefulnomide results in rapid and significant decrease in lefulnomide activity. Rifampicin: Co-administration increases lefulnomide plasma levels. Hepatotoxic drugs: Co-administration may increase side effects. NSAIDs: increase in the free fraction of diclofenac and ibuprof