High Quality Content by WIKIPEDIA articles! 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. A macrolide, sirolimus was first discovered as a product of the bacterium Streptomyces hygroscopicus in a soil sample from Easter Island — an island also known as Rapa Nui, hence the name. It is marketed under the trade name Rapamune by Wyeth.