Sirolimus and everolimus in kidney transplantation.

The mammalian target of rapamycin (mTOR) inhibitors sirolimus and everolimus have shown their efficacy in kidney transplantation, but their wider introduction has been limited by relative high discontinuation rates. Their main advantage compared with calcineurin inhibitors (CNIs) is their relative lack of nephrotoxicity. They differ mainly in pharmacokinetic characteristics and have variable inter- and intra-individual pharmacokinetics. They are metabolized by cytochrome (CYP)-3A4/5 and CYP2C8 enzymes and are substrates for P-glycoprotein (P-gp). Their most important adverse effects are thrombocytopenia, leukopenia, hypercholesterolemia, stomatitis, diarrhea, and, although rare, interstitial pneumonitis. The narrow therapeutic window makes therapeutic drug monitoring (TDM) essential to prevent toxicity or rejection. As we discuss here, the main future challenge is to further optimize mTOR inhibitor (mTORi)-based immunosuppressive therapy.