Medicine & USMLE


  1. Cyclosporine
  2. Tacrolimus
  3. Sirolimus (Rapamycin)
  4. Basiliximab
  5. Mycophenolate


Tacrolimus, also known as FK506, is a drug that causes immunosuppression and prevents transplant rejections. To achieve its effects, tacrolimus binds to FK506 Binding Protein (FKBP) creating a tacrolimus-FKBP complex. This complex then inhibits calcineurin, an enzyme important in the signalling for IL-2 production. By blocking IL-2 production, tacrolimus consequently results in reduced proliferation of all lymphocytes, but especially affects T-cells. Important side effects to note include neurotoxicity, nephrotoxicity, and hyperglycemia. 

Key Points

  • Tacrolimus
    • Also called FK506
    • Immunosuppressant drug
      • Primarily used for transplant rejection prophylaxis
    • Mechanism
      • Inhibits calcineurin by forming a complex with FK506-binding protein (FKBP)
        • Note: Sirolimus also binds FKBP, but at a different site to form a different complex that inhibits mTOR (not calcineurin)
        • Blocks transcription and production of Interleukin-2 (IL-2)
      • Results in reduced proliferation of all lymphocytes (e.g. T cells)
    • Adverse Effects
      • Nephrotoxic
      • Diabetes
      • Neurotoxicity
      • No gingival hyperplasia or hirsutism (contrast vs. Cyclosporine)