A triene macrolide antibiotic isolated from Streptomyces hygroscopicus. Name derived from the native word for Easter Island, Rapa’Nui. Used as an immunosuppressant; antirestenotic. Sirolimus (INN/USAN), also known as rapamycin, is an immunosuppressant drug used to prevent rejection in organ transplantation; it is especially useful in kidney transplants.