Pharmacology · Class
Antiproliferative immunosuppressants !
Drugs that stop immune cells from multiplying by starving them of the building blocks of DNA. Used in transplants and autoimmune disease.
Updated 2026-11-01
What they are
Azathioprine and mycophenolate mofetil interfere with purine synthesis, so dividing lymphocytes cannot copy their DNA. They are combined with calcineurin inhibitors and glucocorticoids after transplantation and used in rheumatoid arthritis, lupus and inflammatory bowel disease.
Mechanism of action
Azathioprine is converted to 6-mercaptopurine and then to thioguanine nucleotides that inhibit purine synthesis and are built into DNA. Mycophenolic acid, the active form of mycophenolate mofetil, inhibits inosine monophosphate dehydrogenase, a key enzyme in the de novo synthesis of guanine nucleotides; B and T lymphocytes depend heavily on this pathway, so they are hit selectively.
Target: Purine synthesis (IMPDH for mycophenolic acid)
Drugs in this class
- AzathioprineAn older immunosuppressant tablet that becomes 6-mercaptopurine and stops immune cells multiplying. Blood counts are…Purine synthesis, through thioguanine nucleotides
- Mycophenolate mofetilAn immunosuppressant used after transplants that blocks an enzyme lymphocytes need to make DNA. It can cause diarrhoea…Inosine monophosphate dehydrogenase (IMPDH)
Others in the class
- ácido micofenólico (micofenolato sódico)
Test yourself
Think of the answer, then tap the question to see it.
Why are lymphocytes more sensitive to mycophenolic acid than most other cells?
They rely on the de novo pathway of guanine nucleotide synthesis, which needs IMPDH; many other cells can use the salvage pathway.
Why is allopurinol dangerous with azathioprine?
Xanthine oxidase inactivates 6-mercaptopurine; allopurinol blocks it, active thioguanine nucleotides accumulate and severe bone marrow suppression can follow.
Which genetic test result predicts severe toxicity with azathioprine?
Low or absent TPMT or NUDT15 activity, which leads to accumulation of thioguanine nucleotides and myelotoxicity.
Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.
Sources: DailyMed - AZATHIOPRINE tablet (DailyMed (U.S. National Library of Medicine), 2026); DailyMed - MYCOPHENOLATE MOFETIL tablet (DailyMed (U.S. National Library of Medicine), 2026); Goodman & Gilman's The Pharmacological Basis of Therapeutics, 14th ed., ch. 39 (McGraw Hill, 2023).
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Representative model, for educational purposes only.