sirolimus

noun

si·​ro·​li·​mus si-ˈrō-li-məs 

: an immunosuppressive drug C₅₁H₇₉NO₁₃ that is a macrocyclic lactone obtained from a soil bacterium of the genus Streptomyces (S. hygroscopicus) and is taken orally especially to prevent rejection of transplanted organs

Sirolimus (also called rapamycin) is a macrolide antibiotic that blocks proliferative responses of lymphocytes to interleukin-2 by inhibiting interleukin-2-mediated signal-transduction events.

—Manuel Pascual et al., The New England Journal of Medicine

called also rapamycin

Note: Sirolimus is often taken in combination with other immunosuppressive drugs (such as cyclosporine) and is marketed under the trademark Rapamune.