Other toxicities include hyperkalemia and hepatotoxicity. Tacrolimus Known during development as FK 506, tacrolimus is a macrolide antibiotic produced by Streptomyces tsukubaensis and has immunosuppressant activity similar to cyclosporine. The drug may produce this effect by binding to the intracellular protein FKBP-12 and is as much as 100 times more potent than cyclosporine with respect to this action. Tacrolimus also suppresses humoral immunity through inhibition of B lymphocyte activation. Metabolized in the liver via the cytochrome P-450 system, tacrolimus is approved for use in liver, renal, heart, bone marrow, and other transplantations.
Toxicity is similar to cyclosporine, with nephrotoxicity being a major adverse effect.
Tacrolimus should not be administered concomitantly with cyclosporine. The drug inhibits nucleic acid synthesis, suppressing cell-mediated hypersensitivity and altering antibody production. Azathioprine is metabolized in the liver and erythrocytes. Renal function has minor effects on levels. The drug causes a dose-dependent reduction in leukocyte and platelet counts.