About Tacrolimus Calcineurin Inhibitor, a macrolide, Immunosuppressant for prevention of graft rejection. Mechanism of Action of Tacrolimus It binds to specific receptors on T cells. It reduces peptidyl-prolyl isomerase activity by forming a complex with immunophilin FKBP-12 (FK506 binding protein).This leads to an increase in intracellular calcium that, in turn, causes a series of reactions inhibiting the transcription of several genes, mainly the cytokines (IL-2, IL-4, and IL-5). It also decreases the production of IL-8 receptor genes and inhibits the production of receptors for IgE molecules. Indications for Tacrolimus 1. Prophylaxis of organ rejection in patients receiving allogenic liver or kidney transplants Interactions for Tacrolimus Increased nephrotoxicity may result if tacrolimus is given with other potentially nephrotoxic drugs like cyclosporin. Avoid concomitant use of potassium-sparing diuretics. Concomitant use of drugs which inhibit the cytochrome P450 (CYP3A)