Rapid killing of tumor cells by cytotoxic therapy, especially in leukemia and lymhomas, can lead to an accelerated release of intracellular potassium, phosphate, and nucleic acid into the circulation. Phosphate binds to calcium, resulting in hypocalcemia, and the nucleic acids are converted to uric acid, resulting in hyperuricemia. This pattern may lead to cardiac arrhythmias and renal and or multiorgan dysfunction. Prevention with hypouricemic drugs (e.g. allopurinol) and IV hydration to maintain a urine flow of 150 to ml per hour prior to treatment is recommended. Alkalization of the urine with bicarbonate is also helpful.