What is being tested?This test measures the amount of mycophenolic acid in the blood. Mycophenolic acid is the active
metabolite of mycophenolate, a drug that is primarily given to patients who have had a heart, kidney, or liver
transplant to help prevent rejection, and secondarily to patients with a variety of
autoimmune disorders. There are two formulations of the drug available, mycophenolate mofetil and mycophenolate sodium.
Mycophenolate is metabolized in the liver to form first the active mycophenolic acid (MPA) and then the inactive mycophenolic acid glucuronide (MPAG). Cells in the body turn some of the MPAG back into MPA. Concentrations of MPA in the blood rise when MPA is first formed and then again when some of it is re-formed. Most MPAG, and small amounts of MPA, are eliminated from the body in the urine.
Normally, a person’s immune system defends the body against infections and can distinguish between “self” and “nonself.” It recognizes a transplanted organ as foreign and begins to attack it. In the case of autoimmune disorders, the immune system mistakenly targets the body’s own cells and tissues. Mycophenolic acid belongs to a group of immunosuppressant drugs and helps to prevent organ rejection, tissue inflammation, and damage. It acts by inhibiting the formation of an enzyme that is necessary for T-lymphocyte and B-lymphocyte proliferation. This causes a decrease in immune system function and in antibody production.
Mycophenolate is given to organ transplant patients in conjunction with other immunosuppressant drugs, such as cyclosporine and tacrolimus. In the treatment of autoimmune disorders, mycophenolate may be used as a single agent (although the patient may also be taking other medications). Like other immunosuppressant agents, mycophenolate may cause side effects and adverse reactions and is associated with an increased risk of infection and the development of lymphoma.
Doctors typically give a standard dose of mycophenolate and then monitor its effect clinically. Most immunosuppressants 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 patient may develop toxicity. However, the therapeutic range for mycophenolic acid has not yet been fully established and physicians can manage most patients symptomatically. When the physician chooses to monitor mycophenolic acid levels, the mycophenolic acid blood test is usually measured as a “trough” level and correlated to clinical side effects. It is timed so that the collection is just prior to the next dose – at the drug’s lowest concentration in the blood.
