The synergistic action of mTOR inhibitors and calcineurin inhibitors (CNIs) provide a rationale for combination therapy, with the potential for CNI-dose reduction and corresponding clinical benefits. CNI therapy is necessary in the early post-transplant phase to deliver sufficient immunosuppressive potency, but use of standard-dose cyclosporine (CsA) with either sirolimus or everolimus has been associated with inferior renal function. Withdrawal of CsA from an mTOR-based regimen reduces renal toxicity, but this may be achieved at the price of increased late rejection and sirolimus-related adverse events. Use of a concentration-controlled mTOR inhibitor with low-exposure CsA seems to be effective in preventing rejection with good renal function. Currently, routine withdrawal of CNIs from an mTOR-inhibitor based regimen, or substitution of an mTOR inhibitor for a CNI, is not justified except in patients who experience toxicity (particularly nephrotoxicity) and who do not respond to CNI dose optimization.
