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Tacrolimus

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Also known as: FK506; TAC
[Often referred to by brand name (see MedlinePlus Drug Information)]
Formal name: Tacrolimus

The Test Sample

What is being tested?

Tacrolimus is an immunosuppressive drug that is given orally or intravenously to people who have had a kidney, liver, heart, or other organ transplant. It is a potent drug that helps to prevent rejection of the transplanted organ by the body. This test measures the amount of tacrolimus in the blood.

Normally, a person's immune system recognizes a new, transplanted organ as foreign and begin to attack it. Tacrolimus limits this response and helps to prevent organ rejection by inhibiting the activation of certain immune cells called T-lymphocytes.

The level of tacrolimus in the blood must be maintained within a narrow therapeutic range. If the concentration is too low, organ rejection may occur; if it is too high, then the person may experience symptoms associated with toxicity.

Dosages must be tailored to the individual. Often, people will begin with higher doses of tacrolimus at the start of therapy and then decrease the dose over the next few weeks.

Tacrolimus is usually taken twice a day at set intervals before or after meals. When a person takes a dose, the blood concentration rises and peaks within about 2 to 3 hours and then begins to slowly drop. The blood test is usually measured as a "trough level," meaning that sample collection is timed for 12 hours post-dose and/or immediately prior to the next dose, when the drug's level in the blood is at its lowest.

How is the sample collected for testing?

A blood sample is obtained by inserting a needle into a vein in the arm.

NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.

Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.

Is any test preparation needed to ensure the quality of the sample?

The sample should be collected 12 hours after the last dose and immediately prior to the next dose or as directed.