Immunosuppressant drugs suppress immune responses, and are widely used in solid organ (kidney, liver, heart and lung), and bone marrow transplantation. They also have a role in treating various autoimmune diseases (rheumatoid arthritis, lupus), allergy, and chronic nephritis.
There are a number of immunosuppressant drugs assayed in Australia. They include the calcineurin inhibitors (CNI), Cyclosporine and Tacrolimus and the mammalian target of rapamycin drugs (mTor), Sirolimus and Everolimus. These drugs are highly bound to erythrocytes and are metabolised by the liver, where they are extensively oxidised by the CYP-3A subfamily of enzymes. Mycophenolate on the other hand, is extensively bound to serum and this is the specimen of choice for Mycophenolate drug assays.
Due to the narrow therapeutic indices of immunosuppressants, the pharmacodynamic variability (intra and inter patient), and the potential for drug interactions, immunosuppressant drug monitoring is necessary to optimise dosing. This is especially important in the case of transplantation to prevent organ rejection, while avoiding over suppression of the immune system.
Immunosuppressant drug testing has been performed by clinical diagnostic
laboratories for over twenty five years. During this time there have been significant advances in the methodologies used to perform testing. The methods commonly used both in Australia and internationally, include immunoassay, HPLC assays and more recently tandem mass spectrometry.