# Calcineurin inhibitors (ciclosporin and tacrolimus Calcineurin inhibitors (ciclosporin and tacrolimus) The calcineurin inhibitors (CNIs) are the mainstay of modern immunosuppressive regimens. CNIs prevent transcription of the IL-2 gene in T cells. As IL-2 is the main T-cell growth factor, inhibition of its production prevents T-cell proliferation. Antiproliferatives Anti-CD25 MPA Azathioprine CD25 Late Proliferation activation mTOR inhibitors Sirolimus Everolimus nephrotoxicity . CNIs have a narrow therapeutic index (a small di ff erence between the minimum e ff ective concentration and the minimum toxic concentration). CNI dosage must therefore be guided by monitoring drug blood levels.