The following medications may affect how allopurinol works or increase the risk of side effects: * aluminum salts (e.g., antacids containing aluminum) * probenecid * salicylates (e.g., ASA) The following medications may be affected by allopurinol: * ampicillin * amoxicillin * azathioprine * chlorpropamide * cyclophosphamide * doxorubicin * bleomycin * procarbazine * mechlorethamine * cyclosporine * mercaptopurine * phenytoin * theophyllines (e.g., aminophylline, oxtriphylline, theophylline) * vidarabine * warfarin