Organ Transplantation - Immunosuppressive Drugs

Dx
Monitor
PGx
Background
Lab Tests

Diagnosis

Indications for Testing

Immunosuppressant dose optimization
Failure to respond to immunosuppressants
Signs or symptoms consistent with inadequate or excessive immunosuppression
Changes to concomitant medications or other variables that affect pharmacokinetics

Monitoring

Therapeutic drug monitoring is required for patients on therapy

Pharmacogenetics and Therapeutic Drug Monitoring

Thiopurine drugs
- Thiopurine methyltransferase (TPMT) activity – use to detect low (abnormal) TPMT activity in individuals who may be at risk for excessive myelosuppression when exposed to standard thiopurine doses such as azathioprine (Imuran^®) and 6-mercaptopurine (Purinethol^®)
  - TPMT phenotype testing does not replace the need for clinical monitoring of patients treated with thiopurine drugs
  - Genotype for TPMT cannot be inferred from TPMT activity (phenotype)
    - Phenotype testing should not be requested for patients currently treated with thiopurine drugs – results will be falsely low
    - Current TPMT phenotype may not reflect future TPMT phenotype, particularly in patients who received blood transfusions within 30-60 days of testing

Clinical Background

Organ transplantation is the strategy of choice for end-stage organ disease. Immunosuppressive therapies have allowed patients to extend the life of the organ but require careful monitoring to prevent toxicity and rejection. Therapeutic ranges and toxic thresholds should be carefully considered based on the clinical setting. Important factors include the organ transplanted, time posttransplant, age and clinical status of the patient, and concomitant medications.

Epidemiology

Prevalence – in 2005, >60,000 patients in the U.S. were living with functioning organ transplants
1-year graft survival rate – ~80-90%

Immunosuppressive Drug Regimens for Organ Transplants

Immunosuppressive Drug Regimens for Organ Transplants
Available Immunosuppressives (immunosuppressive regimen depends on organ transplanted; most common combination is steroid plus calcineurin)	Mechanism of Action	Toxicity	Therapeutic Ranges
Antithymocyte globulin (ATG^®, Atgam^®, Thymoglobulin^®)	Depletes lymphocytes	Increases risk of infection	Aim for 0.1-0.3 lymphocytes/mL
Corticosteroids	Proapoptotic effect on lymphoid cells; suppresses eicosanoid production; increases TGF expression	Increases risk of infection and malignancy (nonmelanoma skin cancers [NMSC])
IL-2 antibodies Daclizumab (Zenapax^®) Basiliximab (Simulect^®)	Selectively blocks IL-2 receptors on T helper cells, preventing T-cell proliferation	Increases risk of malignancy (NMSC and lymphomas)
OKT3 (Muromonab CD3^®)	Depletes lymphocyte T-cells	Increases risk of infection	500-1,500 ng/mL during steady state treatment
Alemtuzumab (Campath-IH)	Targets CD52 on T-cells, B-cells, and NK-cells, causing depletion	Increases risk of infection
Rituximab (Rituxan^®, MabThera^®)	Binds CD20 and B-cells mediating lysis	Increases risk of infection
Belatacept (LEA 29Y)	Binds to T-cells to prevent CD28 signalling	Increases risk of infection
Immunosuppressants
Azathioprine (Imuran^®) 6-mercaptopurine (Puinethol^®)	Inhibits purine nucleotide synthesis, which interferes with DNA synthesis	Increases risk of infection and malignancy (acute myeloid leukemia and myelodysplastic syndromes)
Mycophenolic acid (CellCept^®, Myfortic^®)	Selectively inhibits inosine monophosphate dehydrogenase – interferes with DNA purine synthesis	Increases risk of infection	Measured as trough level; therapeutic range not well established
Sirolimus (Rapamune^®, Rapamycin^®) Everolimus (Certican^®, SDZ-RAD)	Blocks B- and T-cell proliferation by blocking pathway between IL-2 receptor and nucleus; does not block calcineurin pathway; synergistic with cyclosporine	Increases risk of hyperlipidemia and infection	Measured as trough level Sirolimus – 4.0-12.0 ng/mL Everolimus – 3-8 ng/mL
Cyclosporine A (Sandimmune^®, Neoral^®, Gengraf^®)	Inhibits calcineurin phosphatase and reduces IL-2 expression	Increases risk of malignancy, nephrotoxicity, cardiotoxicity, hyperlipidemia	Cyclosporine therapeutic ranges for kidney post-transplant measured 2 hours after first dosing 800-1,700 ng/mL Cyclosporine therapeutic ranges for liver post-transplant 600-1,000 ng/mL
Tacrolimus (Prograf^®FK506)	Inhibits calcineurin phosphatase and reduces IL-2 expression	Increases risk of malignancy, nephrotoxicity, cardiotoxicity, hyperlipidemia	Measured as trough level Tacrolimus therapeutic ranges for kidney and liver 0-2 months post-transplant – 10.0-15.0 ng/mL 3 months and older – 5.0-10.0 ng/mL Tacrolimus therapeutic ranges for heart 0-2 months post-transplant – 10.0-18.0 ng/mL 3 months and older – 8.0-15.0 ng/mL Toxic – ≥26 ng/mL

Indications for Laboratory Testing

Tests generally appear in the order most useful for common clinical situations
Click on number for test-specific information in the ARUP Laboratory Test Directory

Test Name and Number	Recommended Use	Limitations	Follow Up
Cyclosporine A by Tandem Mass Spectrometry 0070035 Method: Quantitative Liquid Chromatography-Tandem Mass Spectrometry	Optimize dosage; monitor compliance	Concentrations determined by mass spectrometry may be 10-50% lower than those observed by immunoassay methods due to greater specificity of the assay for the parent drug
Everolimus by Tandem Mass Spectrometry 0092118 Method: Quantitative Liquid Chromatography-Tandem Mass Spectrometry	Optimize dosage; monitor compliance Optimal therapeutic range for a given patient may differ based on treatment phase (initiation or maintenance), use in combination with other drugs, time of specimen collection relative to prior dose, type of transplanted organ or the therapeutic approach of the transplant center
Mercaptopurine Quantitation, Serum or Plasma 0091084 Method: Quantitative High Performance Liquid Chromatography-Tandem Mass Spectrometry	Monitor compliance	Measures concentration of parent drug only; risk of toxicity associated with TPMT deficiency should be evaluated by TPMT, RBC
Mycophenolic Acid 0090213 Method: High Performance Liquid Chromatography	Optimize dosage; monitor compliance	In vitro conversion of parent drug to mycophenolic acid can occur if specimens are collected shortly after IV administration and could contribute to falsely elevated concentrations of mycophenolic acid Therapeutic ranges and toxic thresholds are not well established
Sirolimus by Tandem Mass Spectrometry 0098467 Method: Quantitative High Performance Liquid Chromatography-Tandem Mass Spectrometry	Optimize dosage; monitor compliance	Concentrations determined by mass spectrometry may be 10-50% lower than those observed by immunoassay methods due to greater specificity of the assay for the parent drug
Tacrolimus by Tandem Mass Spectrometry 0090612 Method: Quantitative Liquid Chromatography-Tandem Mass Spectrometry	Optimize dosage; monitor compliance	Concentrations determined by mass spectrometry may be 10-20% lower than those observed by immunoassay methods due to greater specificity of the assay for the parent drug
Thiopurine Methyltransferase, RBC 0092066 Method: Enzymatic/Quantitative Liquid Chromatography-Tandem Mass Spectrometry	Identify patients at risk for severe toxicity with azathioprine or 6-mercaptopurine	Requires blood sample collected prior to thiopurine drug administration Prefer that the patient has not received a blood transfusion during the two weeks prior to blood collection TPMT enzyme activity can be inhibited by several drugs including the following Naproxen Ibuprofen Ketoprofen Furosemide Sulfasalazine Mesalamine Olsalazine Mefenamic acid Thiazide diuretics Benzoic acid Patients should abstain from these drugs for at least 48 hours prior to TPMT testing in order to avoid falsely low results
Lymphocyte Transplantation CD3 0095949 Method: Quantitative Flow Cytometry	Monitor immunosuppressive therapy with OKT3; test verifies CD3 antigen removal		For testing of immunocompromised patients, order Lymphocyte Subset Panel 4 – T-Cell Subsets Percent and Absolute
Lymphocyte Transplantation Profile 0095798 Method: Quantitative Flow Cytometry	Monitor immunosuppressive therapy with anti-lymphocyte drugs such as OKT3 or ATG (anti-thymocyte globulin)