Which drug is used as an immunosuppressant in organ transplantation, especially in liver transplants?

• A. Methotrexate
• B. Amiodarone
• C. Tacrolimus
• D. Paroxetine

Answer: (C)

Immunosuppression after organ transplantation relies on drugs that specifically block T-cell activation to prevent rejection. Tacrolimus is a calcineurin inhibitor that binds to the immunophilin FKBP-12; this complex inhibits calcineurin, reducing transcription of interleukin-2 and other cytokines. With less IL-2, T-cell proliferation and activation are suppressed, which helps the body accept the transplanted organ. In liver transplants, tacrolimus is a cornerstone therapy because it effectively lowers rejection risk and is used long-term, typically alongside other immunosuppressants. The other drugs listed do not serve this role: methotrexate is a chemotherapy/antimetabolite not used as a primary transplant immunosuppressant, amiodarone is an antiarrhythmic with potential liver toxicity, and paroxetine is an antidepressant.