One of the antimetabolite group of drugs (see ANTIMETABOLITES), which includes methotrexate, ﬂuorouracil and thioguanine. These drugs are incorporated into new nuclear material in the cell or combine irreversibly with vital cellular enzymes, preventing normal cellular metabolism and division. Mercaptopurine is used mainly for the maintenance treatment of acute LEUKAEMIA, though it is increasingly proving valuable in the treatment of CROHN’S DISEASE. As with all CYTOTOXIC drugs, dosage must be carefully controlled; in particular it must be reduced if used concurrently with allopurinol. Side-eﬀects include gastrointestinal upsets (including ulceration), and bone-marrow depression.
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