Tacrolimus monohydrate (Tacrolimus, FK506) is a macrolide antibiotic that primarily acts as an inhibitor of calcineurin phosphatase by binding to FK506 binding protein (FKBP). This inhibition blocks calcium-dependent processes, including interleukin-2 gene transcription, nitric oxide synthase activation, cell degranulation, and apoptosis, and also has immunosuppressive, neuroregenerative and neuroprotective properties.