Tacrotor 0.03%

Tacrolimus is a macrolide lactone immunosuppressant and calcineurin inhibitor primarily used to prevent organ rejection in patients receiving kidney, liver, heart, or lung transplants.[1] It works by binding to the intracellular protein FKBP12, forming a complex that inhibits the phosphatase activity of calcineurin, thereby blocking the dephosphorylation and nuclear translocation of nuclear factor of activated T-cells (NFAT), which suppresses T-cell activation, proliferation, and the production of cytokines such as interleukin-2 (IL-2).[1] Discovered in 1984 from the fermentation broth of the soil bacterium Streptomyces tsukubaensis isolated near Mount Tsukuba in Japan, tacrolimus (also known as FK506) was developed by Fujisawa Pharmaceutical Company as a more potent alternative to cyclosporine for immunosuppression.[2] Its chemical formula is C44H69NO12, and it exhibits low oral bioavailability (approximately 20-25%), necessitating therapeutic drug monitoring to maintain trough levels between 5-15 ng/mL depending on the transplant type and time post-transplant.[2][1]