Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. Tacrolimus (also FK-506 or Fujimycin) is an immunosuppressive drug whose main use is after allogeneic organ transplant to reduce the activity of the patient''s immune system and so lower the risk of organ rejection. It reduces interleukin-2 (IL-2) production by T-cells. It is also used in a topical preparation in the treatment of severe atopic dermatitis (eczema), severe refractory uveitis after bone marrow transplants, and the skin condition vitiligo. It is a 23-membered macrolide lactone discovered in 1984 from the fermentation broth of a Japanese soil sample that contained the bacteria Streptomyces tsukubaensis.