Tacrolimus-d3 (FK506-d3) is deuterium labeled Tacrolimus. Tacrolimus (FK506), a macrocyclic lactone, binds to FK506 binding protein (FKBP) to form a complex. Tacrolimus inhibits calcineurin phosphatase, which inhibits T-lymphocyte signal transduction and IL-2 transcription. Immunosuppressive properties[1].