A drug used to prevent the rejection of organ and bone marrow transplants by the body. Rapamycin is an antibiotic that blocks a protein involved in cell division and inhibits the growth and function of certain T cells of the immune system involved in the body's rejection of foreign tissues and organs. It is a type of immunosuppressant and a type of serine/threonine kinase inhibitor. Rapamycin is now called sirolimus.
