test-icon Tacrolimus – LC-MS/MS:

(Assayed daily, Monday to Friday)

Tacrolimus monitoring is recommended for all patients receiving immunosuppression with Prograf for preventing graft rejection or autoimmune-based disorders. The drug was previously known as FK506. A slow release formulation (Advagraf) was introduced in 2008 for once-daily dosing. Other formulations include Modigraf (granules designed for small doses in water) and Adoport (generic tacrolimus) both of which were introduced in 2010, and also Capexion, Tacni, and Vivadex.

Turnaround: >95% of samples are turned around within 24 h of receipt on weekdays. We aim to issue results by 4 pm on samples received by 1.30 pm and, depending on workload, by 5–6 pm for samples received up to 2.30 pm
Sample: 2 mL EDTA-anticoagulated whole blood just pre-dose (12 h / 24 h post-dose for twice / once daily dosing, respectively)
Method: Liquid chromatography-tandem mass spectrometry
Principle: Tacrolimus is measured in whole blood using liquid chromatography-tandem mass spectrometry (LC-MS/MS) based on a method by Keevil et al. (Annals of Clinical Biochemistry 2002; 39: 487–492). Our validated method is rapid, requires only a small sample volume, and offers advantages over immunoassay methods (Brown et al., Clinical Chemistry 2005; 51: 586–592). The IDM laboratory participates in the International Proficiency Testing Scheme for tacrolimus.

Immunosuppressive drugs require monitoring because they act within a narrow range of concentrations and show large inter-individual differences in drug handling and efficacy which make standard dosing regimens impractical. Therapy aims to suppress the immune system sufficiently to prevent graft rejection or autoimmune disease but without either acute toxicity (e.g. renal or gastrointestinal damage) or the increased generic risks of infection or malignancy. IDM provides the most valuable method for regulating dosage in these circumstances and because no real time measurement of “immunosuppression” exists. The principle is to adjust dosage on the basis of standardised drug level measurements that can be targeted to a therapeutic range appropriate for the individual patient. Such adjustments must be made in conjunction with clinical information and other laboratory test results. IDM therapeutic ranges may vary with:

  • the indication for drug therapy (reflecting disease or transplant history)
  • time after the operation
  • co-therapy with other immunosuppressive agents.

The customary single blood sample used for monitoring is the trough drug level, determined just prior to dosage and at a constant interval from the time of the previous dose. Measurements at alternative times, e.g. 2 hours post dose (C2), may be useful in certain situations. For ciclosporin in particular, a C2 level might offer an improved estimate of total early drug exposure. However, it may be difficult to obtain accurately if dosage and phlebotomy times vary. Therapeutic ranges are higher for C2 than for trough drug levels because drug concentrations peak at around 2 h post dose. Contact the IDM Laboratory for more information if required.

Immunosuppressive drug concentrations may also be profoundly affected by:

  • co-medication – especially cytochrome P450 inducers and inhibitors for tacrolimus, ciclosporin sirolimus and everolimus (e.g. rifampicin, corticosteroids and antifungal or antiviral agents) and antiviral co-therapy (e.g. ganciclovir, aciclovir); oral antibiotics and changing ciclosporin or tacrolimus levels (or inter-conversion) for mycophenolate;
  • organ function, especially liver function for tacrolimus and ciclosporin, and renal function for mycophenolate;
  • gastrointestinal dysfunction and haemodynamic instability;
  • hypoalbuminaemia and low haematocrit – increasing free drug levels (and often toxicity);
  • genetic variability between individuals e.g. in the expression of cytochrome P450 3A or p-glycoprotein for tacrolimus, ciclosporin or sirolimus, and of UDP-glucuronyltransferase (UDPGT) 1A8/9 for mycophenolate;
  • non-prescription substances such as St John’s wort and grapefruit juice.

In addition to use as an immunosuppressant, everolimus is being used as an antitumour drug and has been licensed for use in treating advanced renal cell carcinoma with the alternate trade name of Afinitor. Currently there is no information available on a suitable therapeutic range for these effects.

The frequency at which IDM is performed generally decreases with time after transplant. It is rarely necessary to monitor levels more than three times weekly e.g. Monday, Wednesday and Friday, because the half-lives of the immunosuppressants exceed 12 h. Consequently, drug levels will not re-equilibrate for 2–3 days after changes in dosage. However, immediately after transplantation, daily monitoring may be required in unstable (especially paediatric) patients but the frequency may decrease to once three or six monthly in long-term stable patients. The frequency of testing should be determined by any changes in likely modulators of drug levels, that is:

  • if immunosuppressive drug dosage is increased or decreased on clinical grounds;
  • if the formulation of the drug is changed e.g. Prograf to Advagraf / Modigraf / Adoport, Neoral to Deximmune, CellCept to Arzip / Myfenax;
  • if acute graft rejection is diagnosed;
  • if any other type of graft dysfunction occurs or is suspected;
  • if drug-related side-effects are detected (e.g. nephro- or neurotoxicity for tacrolimus or ciclosporin, gastrointestinal disturbance for mycophenolate);
  • if co-medication affecting drug levels is introduced, tapered or withdrawn;
  • if liver or renal function additionally deteriorates or improves;
  • if non-adherence is suspected;
  • if diarrhoea or persistent severe gastrointestinal dysfunction occurs.

The examination of drug profiles during a dosage interval may be a valuable adjunct to conventional trough level monitoring. The additional information available from these pharmacokinetic studies may reveal unexpected abnormalities in the rate and extent of drug absorption and disposition.

time-icon Turnaround: within 24hrs
price-icon Price: Contact Lab
contact-icon Contacts
IDM service: kch-tr.KCHIDMService@nhs.net
ref-range-icon Reference Ranges
Therapeutic Ranges: (males = females)
NB. These ranges are meant only as a guide and will need to be considered in the context of clinical indications and any additional immunosuppressive therapy that is prescribed.

12 – 18 µg/L (ng/mL) occasionally higher:
  • Small bowel graft recipients (alone or with another graft) in month 1 post transplant.
8 – 12 µg/L (ng/mL) occasionally 15 µg/L:
  • Liver, renal, cardiac and other graft recipients during the first post-operative month.
  • Renal, cardiac and other non-liver graft recipients thereafter.
  • Treatment of graft-versus host disease for months 1–3.
  • Treatment of autoimmune disease (for induction).
5 – 10 µg/L (ng/mL):
  • Liver graft recipients months 1–3.
  • Treatment of graft versus-host disease after month 3.
  • Some long-term, stable renal allograft recipients.
1 – 8 µg/L (ng/mL):
  • Long-term, stable liver graft recipients.
  • Some long-term, stable recipients of non-liver grafts.
  • Responsive patients with autoimmune disease.