Pancytopenia due to the interaction of allopurinol with azathioprine or mercaptopurine.
(1) Allopurinol increases the haematological toxicity of azathioprine and mercaptopurine, with a risk of pancytopenia.  (2) Combination of allopurinol with azathioprine or mercaptopurine should be avoided.
D000493:Allopurinol / Q000009:adverse effects; D000963:Antimetabolites / Q000009:adverse effects; D000075202:Contraindications; D004347:Drug Interactions; D006801:Humans; D015122:Mercaptopurine / Q000009:adverse effects; D010198:Pancytopenia / Q000209:etiology; D016896:Treatment Outcome
D000963:Antimetabolites; D000493:Allopurinol; D015122:Mercaptopurine