Renal & hepatic impairment. NUDT15 mutation. Do not receive immunizations w/ live organism vaccine until at least 3 mth after the end of azathioprine treatment. Bone marrow depression. Discontinue therapy if jaundice becomes apparent. Monitor CBC including platelet levels during 1st 8 wk of therapy & repeat mthly or at intervals of ≤3 mth if high dosage is used or if severe renal &/or hepatic disorders are present; hematological response; LFT. Inherited deficiency of enzyme thiopurine methyltransferase (TPMT). Not beneficial to patients w/ Lesch-Nyhan syndrome. Chromosomal abnormalities. Increased risk of non-Hodgkin's lymphomas, other malignancies. Avoid exposure to UV & sunlight. W/hold therapy at 1st sign suggestive of progressive multifocal leukoencephalopathy. HBV & varicella zoster virus infection.