TACROLIMUS (FK506)

Code
900.4010
Name
TACROLIMUS (FK506)
Category
None
Department
Send-Out
Start Date
Expiration Date
Synonyms
FK506;PROGRAF
CPT Codes
80197
Site
SBMF
Reference Test
30060
ATLAS Test Code

Specimen Information

Type

Lavender, EDTA, WHOLE BLOOD

Volume

2.0 ml

Transport Info

Refrigerated

Fasting Required?
False
Patient Instructions

Reference Range

See Report

Methodology

Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS)

Clinical Significance

Monitor concentrations of tacrolimus primarily to prevent nephrotoxicity.
Tacrolimus is an immunosuppressive drug discovered in 1984 by the Fujisawa Pharmaceutical Co., Ltd. It has been shown to be effective for the treatment of rejection following transplantation. The results of clinical trials with liver and kidney have been published and clinical studies are continuing for a variety of indications.The mode of action for tacrolimus is under active investigation. Tacrolimus binds a family of proteins termed FK506 binding proteins (FKBP’s). The formation of a larger pentameric complex comprised of FKBP, tacrolimus, calmodulin and calcineurins A and B results in the inhibition of the phosphatase activity of calcineurin. The action of transcription factors requiring dephosphorylation for transport to the cell nucleus is thus inhibited leading to blockage of T-cell proliferation and function.Pharpacokinetic studies with tacrolimus have shown that there are large inter- and intra-individual differences in its kinetics in organ transplant patients. Studies have also indicated that whole blood rather than plasma may serve as the more appropriate medium to describe the pharmacokinetic characteristics of tacrolimus. Tacrolimus is bound to proteins, mainly albumins, and alpha-1-acid glycoprotein, and is highly bound to erythrocytes.Tacrolimus is extensively metabolized in the liver and small intestine microsomes utilizing the hepatic cytochrome enzymes. Nine different metabolites of tacrolimus have been identified; several of the metabolites have been found and tested in whole blood. At the present time it is not clear whether the nephrotoxicity of tacrolimus is the result of parent drug, metabolites, or a combination of both. The use of tacrolimus is associated with serious toxic side effects, primarily nephrotoxicity. Other adverse side effects include neurotoxicity, hypertension, insomnia and nausea.

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