[Leflunomide--a new drug for pharmacological immunomodulation].

The novel immunomodulatory agent leflunomide exhibits a strong anti-inflammatory action. This isoxazole derivative is chemically unrelated to any hitherto applied immunosuppressants. As a prodrug leflunomide is completely converted to its active metabolite A 77 1726 (M1) which blocks the dihydroorotate dehydrogenase, a key enzyme of the pyrimidine de novo synthesis. Drug-related adverse effects are mild, dose-related and reversible, characterising leflunomide as a safe immunosuppressant. While up to now leflunomide has just been approved for therapy of rheumatoid arthritis, its mechanism of action affects multiple inflammatory pathways, thereby suggesting it to be a potent therapeutic agent in autoimmune diseases, graft rejection, and tumour therapy. First dermatological experience has been gained in psoriasis and bullous pemphigoid. The role of leflunomide in the dermatologist's therapeutic armamentarium will evolve during the next years.