Introduction
High-dose methotrexate (MTX) therapy is an important component of chemotherapy regimens for acute lymphoblastic leukemia, lymphoma, osteosarcoma, and other cancers [1]. One of the primary adverse effects of high-dose MTX therapy is renal injury [1], [2] and [3]. Both volume expansion to maintain adequate urine flow and urinary alkalinization are essential for preventing MTX-induced nephrotoxicity [2] and [3]. One study in adults demonstrated that maintaining urinary pH > 7.0 was effective for reducing nephrotoxicity during high-dose MTX therapy [4]; while another in children found that low urinary pH (< 6.5) was associated with higher plasma MTX concentrations and toxicity [5]. Therefore protocols for high-dose MTX therapy call for maintaining urinary pH > 7 or > 8 with bicarbonate therapy [2] and [3]. Intravenous hydration with sodium bicarbonate is adjusted to keep urine pH within protocol guidelines; with urine samples sent for pH measurement with every void during hospitalization.