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

At a Glance

Why Get Tested?

To determine the level of the drug tacrolimus in your blood in order to establish a dosing regimen, maintain therapeutic levels, and detect toxic levels

When to Get Tested?

As soon as tacrolimus therapy begins, frequently at first, then at regular intervals to monitor concentrations over time

Sample Required?

A blood sample drawn from a vein in your arm

Test Preparation Needed?

The sample should be collected 12 hours after your last dose and immediately prior to your next dose or as directed by your health practitioner.

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.

The Test

Common Questions

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Article Sources

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NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.

Sources Used in Current Review

Prograf. Rx List. Available online at http://www.rxlist.com/prograf-drug.htm through http://www.rxlist.com. Last reviewed September 23, 2013. Accessed February 26, 2014.

Patient Information. Prograf. Astellas Pharma Inc. Available online at http://www.prograf.com/Docs/13H057-PRG-WPI-PPI.pdf through http://www.prograf.com. Accessed February 26, 2014.

Tacrolimus (Oral Route). Mayo Clinic. Available online at http://www.mayoclinic.org/drugs-supplements/tacrolimus-oral-route/description/drg-20068314 through http://www.mayoclinic.org. Last updated December 1, 2013. Accessed February 26, 2104.

Sources Used in Previous Reviews

Clarke, W. and Dufour, D. R., Editors (2006). Contemporary Practice in Clinical Chemistry. AACC Press, Washington, DC. McMillin, G. and Hammett-Stabler, C. Chapter 39: Therapeutic Drug Monitoring, Pp 453-463.

(2007 April 1). Tacrolimus. MedlinePlus Drug Information [On-line information].  Available online at http://www.nlm.nih.gov/medlineplus/druginfo/medmaster/a601117.html. Accessed on 6/9/07.

Aradhye, S., et. al. (2006 December, Revised). Medicines for Keeping Your New Kidney Healthy. American Society of Transplantation [On-line information]. PDF available for download at http://www.a-s-t.org/files/pdf/patient_education/english/AST-EdBroKIDNEYMED-ENG.pdf through http://www.a-s-t.org. Accessed on 6/9/07.

(2006 July 1, Revised). Tacrolimus Topical. MedlinePlus Drug Information [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/druginfo/medmaster/a602020.html. Accessed on 6/9/07.

Howard, A. (2004 July 12). Long-Term Monitoring and Care of the Kidney Transplant Recipient. Medscape Transplantation 5(2), 2004 [On-line article]. Available online at http://www.medscape.com/viewarticle/481411 through http://www.medscape.com. Accessed on 6/9/07.

Kim, J. Cyclosporine and Tacrolimus Toxicities. Kidney Transplant Program, Univ of Southern California Department of Surgery [On-line information]. Available online at http://www.kidneytransplant.org/article-cyclosporineandtacrolimustoxicities.html through http://www.kidneytransplant.org. Accessed on 6/9/07.

(© 2007). Tacrolimus. ARUP's Laboratory Test Directory [On-line information]. Available online at http://www.aruplab.com/TestDirectory/clinical_guide.jsp through http://www.aruplab.com. Accessed on 6/16/07.

(© 2007). Tacrolimus. LabCorp's On-line Directory of Services and Interpretive Guide [On-line information]. Available online at http://www.labcorp.com/datasets/labcorp/html/chapter/ through http://www.labcorp.com. Accessed on 6/16/07.

(2006 April, Revised). Prograf. FDA MedWatch [On-line information]. PDF available for download at http://www.fda.gov/medwatch/SAFETY/2006/Apr_PIs/Prograf_PI.pdf through http://www.fda.gov. Accessed on 6/16/07.

(2007 April 1). Tacrolimus (Oral Route, Intravenous Route). Mayoclinic.com [On-line information]. Available online at http://www.mayoclinic.com/health/drug-information/DR601851 through http://www.mayoclinic.com. Accessed on 6/10/07.

Woo, D. and James, W. (2005 May 24). Topical Tacrolimus: A Review of Its Uses in Dermatology. Medscape from Dermatitis 2005;16(1):6-21 [On-line article]. Available online at http://www.medscape.com/viewarticle/505242 through http://www.medscape.com. Accessed on 6/9/07.

(2001). Therapeutic Drug Monitoring: Is it Important for Newer Immunosuppressive Agents? Medscape from Drug Ther Perspect 17(22):8-12, 2001 [On-line information]. Available online at http://www.medscape.com/viewarticle/414907 through http://www.medscape.com. Accessed on 6/9/07.

Martindale, The Complete Drug Reference (Online information). Available online at http://www.thomsonhc.com/hcs/librarian/PFDefaultActionId/pf.PrintReady through http://www.thomsonhc.com. Accessed August 2007.

(June 1, 2008) MedlinePlus Drug Information. Tacrolimus. Available online at http://www.nlm.nih.gov/medlineplus/druginfo/meds/a601117.html. Accessed March 2011.

(February 1, 2011) Mayo Clinic. Tacrolimus. Available online at http://www.mayoclinic.com/health/drug-information/DR601851 through http://www.mayoclinic.com. Accessed March 2011.

(December 4, 2007) United Network for Organ Sharing. Transplant Living: Medications, Tacrolimus. AVailable online through http://www.transplantliving.org. Accessed March 2011.

Henry's Clinical Diagnosis and Management by Laboratory Methods. 21st ed. McPherson R, Pincus M, eds. Philadelphia, PA: Saunders Elsevier: 2007, Pp 317-318.

Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. Burtis CA, Ashwood ER, Bruns DE, eds. St. Louis: Elsevier Saunders; 2006, Pp 1279-1280.

Clarke, W. and Dufour, D. R., Editors (2006). Contemporary Practice in Clinical Chemistry. AACC Press, Washington, DC. McMillin, G. and Hammett-Stabler, C. Chapter 39: Therapeutic Drug Monitoring, Pg 453-463.

(September 8, 2008) Lemi L. Transplants, Liver. eMedicine article. Available online at http://emedicine.medscape.com/article/776313-overview through http://emedicine.medscape.com. Accessed March 2011.