Tacrolimus (Blood)

Diagnostic Use

Tacrolimus is an immunosuppressive agent which selectively inhibits T lymphocyte proliferation.

• If the patient has human anti-mouse antibodies (HAMA) this may interfere with the tacrolimus test. The anti-rejection drug OKT3 may cause HAMA.
• Substances that alter the activity of  cytochrome P-450 3A4 will cause tacrolimus to be metabolised at a different rate: madazole mycotics such as  clotrimazole, fluconazole, and ketoconazole and macrolide antibiotics such as clarithromycin and erythromycin have been reported to increase the plasma concentration of tacrolimus.
• Danazol and omeprazole have also been reported to increase the plasma concentration of tacrolimus.
• Rifampicin has been reported to cause a decrease in the concentration of tacrolimus measured in blood.
• Plasma levels of tacrolimus may increase or decrease following administration of methylprednisone.

Reference Intervals

The quoted therapeutic range is for trough concentrations; specimens should be collected shortly before administering the next dose of the drug.

The general guidance for target trough concentration is 5-15ug/L, although clinical circumstances may indicate a higher or lower target.

It takes at least two days of therapy to reach steady state conditions.