UCLA

Sirolimus is a macrocyclic antibiotic, which binds to the FK binding protein and modulates the activity of mTOR (mammalian target of rapamycin). This drug is widely used for preventing rejection of solid organ transplants and graft vs. host disease following bone marrow transplantation. A unique feature of sirolimus is that it also induces profound microcytosis, which is poorly understood. Previous studies have demonstrated that oral iron supplementation in patients who received sirolimus did not improve their microcytic anemia. However, anemia improved once patients discontinued sirolimus. We hypothesize that functional iron deficiency is one of the mechanisms by which sirolimus induces microcytic anemia and that this is due to sirolimus' impact on hepcidin. A retrospective chart review was done as well as a prospective study to determine the prevalence and characteristics of sirolimus-induced anemia in renal transplant patients.