Pharmacology · Class
Calcineurin inhibitors !
Transplant medicines that stop T cells from switching on by blocking calcineurin. Their blood levels are measured, and they can harm the kidneys.
Updated 2026-11-01
What they are
The backbone of maintenance immunosuppression after kidney, liver and heart transplantation: ciclosporin and tacrolimus. Ciclosporin is also used for severe psoriasis and rheumatoid arthritis; both are used off label in some inflammatory bowel disease.
Mechanism of action
Each drug first binds an immunophilin inside the T cell: ciclosporin binds cyclophilin, tacrolimus binds FKBP12. The drug-immunophilin complex blocks calcineurin, a calcium-dependent phosphatase. Without calcineurin, the transcription factor NFAT stays phosphorylated in the cytoplasm, the IL-2 gene is not switched on, and T cells do not proliferate in response to the graft.
Target: Calcineurin (protein phosphatase 2B), reached through cyclophilin or FKBP12
Drugs in this class
- CiclosporinA transplant medicine that keeps T cells from attacking the new organ. Its blood level is measured, and it can raise…Calcineurin, through cyclophilin A
- TacrolimusThe most used anti-rejection drug after transplants. It blocks T-cell activation; its level is measured, and it can…Calcineurin, through FKBP12
Others in the class
- voclosporina
Test yourself
Think of the answer, then tap the question to see it.
Which protein does each calcineurin inhibitor bind before it can block calcineurin?
Ciclosporin binds cyclophilin and tacrolimus binds FKBP12; the drug-immunophilin complex is what inhibits calcineurin.
How does blocking calcineurin stop T-cell activation?
Calcineurin dephosphorylates NFAT so it can enter the nucleus; without it NFAT stays in the cytoplasm and IL-2 and other cytokine genes are not transcribed.
A transplant patient on tacrolimus starts clarithromycin. What can happen?
Clarithromycin inhibits CYP3A4, so tacrolimus levels rise, with risk of nephrotoxicity, neurotoxicity and hyperkalaemia; levels are checked closely.
Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.
Sources: DailyMed - TACROLIMUS capsule (DailyMed (U.S. National Library of Medicine), 2025); DailyMed - CYCLOSPORINE solution (DailyMed (U.S. National Library of Medicine), 2025); Goodman & Gilman's The Pharmacological Basis of Therapeutics, 14th ed., ch. 39 (McGraw Hill, 2023).
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Representative model, for educational purposes only.