Azathioprine and MMF
Azathioprine and MMF for SLE
Azathioprine is a purine antagonist, which is converted into 6-mercaptopurine and thioinosine monophosphate (TIMP). The latter inhibits cellular replication by reducing purine synthesis. By this action the drug inhibits cytotoxic T-cell proliferation.
Mycophenolate mofetil (MMF) acts in the similar pathway of purine synthesis, yet by inhibiting the enzyme inosine monophosphate (IMP) dehydrogenase.
Azathioprine is used for lupus nephritis in order to reduce glucocorticoid requirement. It is given with corticosteroids to decrease mortality and to slow down progression to end stage renal disease. It is considered less effective than cyclophosphamide, but it is also less toxic.
Due to the unspecific mechanism of action, azathioprine has significant adverse effects, including bone marrow suppression (leukopenia, thrombocytopenia, anemia), GI-complaints, pancreatitis and hepatotoxicity. Monthly blood counts and liver function should be obtained. It is a carcinogenic drug.
What is NOT true regarding azathioprine therapy?
Extra info: Azathioprine and its metabolites do cross the placenta. Since azathioprine is a mutagen and possibly a carcinogen, this drug should not be used during pregnancy.