In circumstances of kidney injury that occur despite appropriate precautions of hydration and urine alkalization, leucovorin rescue will NOT be of benefit, because leucovorin acts intracellularly and renal toxicity is a mechanism of extracellular methotrexate crystallization within the renal tubules. Rescue can be achieved with glucarpidase, a recombinant carboxypeptidase that enzymatically and rapidly cleaves MTX to form the amino acid glutamate and soluble 2,4-diamino-N10-methylpteroic acid (DAMPA). It is important to note that depending on the MTX assay being used to monitor blood levels, DAMPA may provide a false-positive until eliminated from the body. As glucarpidase will also act on extracellular leucovorin, leucovorin should not be administered within 2 hours before or after glucarpidase administration.