thioguanine /thī′ōgwä″nēn/ , a purine analog antagonist, an antineoplastic that acts as an antimetabolite. 
INDICATIONS: It is prescribed in the treatment of a variety of malignant neoplastic diseases, especially acute and chronic myelogenous leukemias. CONTRAINDICATIONS: Known hypersensitivity or resistance to this drug prohibits its use. It is not given during pregnancy. ADVERSE EFFECTS: Among the most serious adverse effects are bone marrow depression, GI distress, and stomatitis.
