Tacrolimus is a macrolide, one of a group of bactericidal antibiotics that act by binding to the 50S ribosomal subunit and inhibiting protein synthesis. It is an immunosuppressive drug that is mainly used after allogeneic organ transplant to reduce the activity of the patient’s immune system and so lower the risk of organ rejection. It is also used in a topical preparation in the treatment of atopic dermatitis (eczema), severe refractory uveitis after bone marrow transplants, exacerbations of minimal change disease, and the skin condition vitiligo.