Tacrolimus is a 23-membered macrolide lactone. It is an immunosuppressive drug whose main use is after allogenic organ transplant to reduce the activity of the patient's immune system and so the risk of organ rejection. Tacrolimus inhibits T-lymphocyte activation. Experimental evidence suggests that tacrolimus binds to an intracellular protein, FKBP-12. A complex of tacrolimus-FKBP-12, calcium, calmodulin, and calcineurin is then formed and the phosphatase activity of calcineurin inhibited. This effect may prevent the dephosphorylation and translocation of nuclear factor of activated T-cells (NF-AT), a nuclear component thought to initiate gene transcription for the formation of lymphokines (such as interleukin-2, gamma interferon).
The net result is the inhibition of T-lymphocyte activation (i.e., immunosuppression).
Tacrolimus is indicated for the prophylaxis of organ rejection in patients receiving organ transplant.