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Tacrolimus, or fujimycin, is an immune-suppressing drug mainly prescribed after organ transplants to reduce the risk of transplant rejection. Isolated from a Japanese soil sample containing Streptomyces tsukubaensis, the drug name tacrolimus was derived from the phrase "Tsukuba macrolide immunosuppressant." First approved by the Food and Drug Administration (FDA) in 1994, the medication has been used for patients receiving liver, heart, pancreas, kidney, lung, small bowel, cornea, skin, bone marrow, trachea, and limb transplants. The drug works by inhibiting the body’s production of interleukin-2, a chemical mediator implicated in acute rejection episodes and inflammation. Physicians also prescribe this medication to treat inflammation associated with ulcerative colitis, autoimmune skin conditions, and severe eye inflammation.
Generally, tacrolimus has similar immune-suppressing characteristics to the more commonly used post-transplant drug cyclosporin, but it delivers a more potent effect with equal volumes of drug. Immunosuppression using this medication has produced a lower rate of transplant rejection compared to that of cyclosporin — 30.7 percent versus 46.4 percent — according to one clinical study. Outcomes in liver transplant patients are better with tacrolimus than with cyclosporin in the first year after transplantation. Tacrolimus is typically prescribed in a post-transplant cocktail with other drugs. Initial doses range from 0.15 milligrams to 0.20 milligrams per kilogram of body weight in a daily infusion.
In the ointment form, tacrolimus may be used to treat eczema. Its mode of action and potency are similar to that of a steroid. An advantage of this medication over the steroid is that it does not cause atrophy of the skin. It can, therefore, be used continuously on even the thinner skin areas of the face and eyelids. The ointment has also been used to treat segmental vitiligo, especially on the face.
The main side-effects of using the drug, which can be severe, include headache, cardiac damage, blurred vision, liver and kidney problems, seizures, and diabetes. In addition, fungal and viral infections are more difficult to manage. Side-effects occur with both intravenous and oral administration of the drug and may require a reduction in the dose used. Elevated blood glucose levels may require administration of insulin. Among patients taking tacrolimus, the proportion reporting more than one side-effect is about 99.8 percent.
In patients receiving immunosuppressants to prevent transplant rejection, malignancy is a known possibility. Pregnant or breast-feeding mothers and infants should not take tacrolimus. Other contraindications for the drug include severe liver or kidney disease, active infections, cancers, and acute heart disease. Patients must be cautious when getting sun exposure due to the photo-sensitizing effect of this medication. Grapefruit juice can also increase the drug effects.