mTOR inhibition: the learning curve in kidney transplantation.

All immunosuppressive medications require a learning curve that enables clinicians to improve the therapeutic index of agents. Mammalian target of rapamycin (mTOR) inhibitors are potentially a less nephrotoxic form of immunosuppression than calcineurin inhibitors (CNIs) that has been used in kidney transplant recipients for more than two decades. This drug class has a novel immunosuppressive action, probably mediated in part through inhibition of growth receptor signaling mechanisms. In addition, it has a unique drug toxicity, which is partially dose-related. This medication class also possesses antiproliferative activity, which may be useful in-post-transplant patients with increased atherosclerotic and malignancy risks. mTOR inhibitors have been utilized for de novo immunosuppression with CNIs, corticosteroids, and antimetabolites. mTOR inhibitors also have been used as CNI-sparing agents both early and late post-transplant. Much debate remains over how to best utilize mTOR inhibition in kidney transplantation.