Glucarpidase + Methotrexate + Leucovorin

Glucarpidase + methotrexate + leucovorin is a therapeutic combination used in the management of high-dose methotrexate toxicity, particularly in patients who develop renal dysfunction. **Mechanism and Clinical Use** Glucarpidase (brand name Voraxaze) is a recombinant bacterial enzyme that rapidly hydrolyzes methotrexate into inactive metabolites, specifically 2,4-diamino-N10-methylpteroic acid (DAMPA)[5]. When administered, glucarpidase can lower methotrexate levels by ≥97% within 15 minutes, providing a non-renal route of elimination for methotrexate in patients with impaired kidney function[2][5]. Methotrexate is an antimetabolite that inhibits dihydrofolate reductase, preventing the conversion of folic acid to its active form. High-dose methotrexate (HDMTX) therapy can lead to nephrotoxicity and delayed methotrexate clearance, which increases the risk of severe toxicities[1][3]. Leucovorin (folinic acid) acts as a "rescue" agent by providing normal cells with folates needed for DNA synthesis, thereby protecting them from methotrexate toxicity[8]. It's typically initiated 24-36 hours after methotrexate infusion and continued until methotrexate clearance[8]. **Administration Guidelines** The combination therapy follows specific protocols: 1. **Glucarpidase administration**: Recommended at 50 units/kg when methotrexate concentrations are >1 μmol/L in patients with delayed clearance due to impaired renal function[1][5]. Even partial doses should be given if the full dose is unavailable[1]. 2. **Leucovorin scheduling**: Should not be administered within 2 hours before or after glucarpidase, as glucarpidase will cleave leucovorin as well as methotrexate[1][5]. Leucovorin rescue should be reinitiated no sooner than 2 hours after glucarpidase administration[1]. 3. **Continued supportive care**: Standard supportive measures including hydration and urine alkalization should be continued throughout treatment[5]. **Clinical Efficacy** Early intervention with the combination of leucovorin and glucarpidase has been shown to be highly effective in patients who develop HDMTX-induced renal dysfunction[3]. In clinical studies, plasma methotrexate concentrations decreased by 98.7% within 15 minutes of glucarpidase administration[3]. However, it's important to note that glucarpidase will not reverse toxicities present prior to its administration[5]. The therapy is most effective when glucarpidase is given within 96 hours of methotrexate administration[3][5]. Severe toxicity and mortality have been observed in patients where glucarpidase rescue was delayed[3]. **Risk Factors and Monitoring** Factors associated with severe toxicity include: - Grade 4 toxicity before glucarpidase administration - Inadequate initial increase in leucovorin dosing - Administration of glucarpidase more than 96 hours after methotrexate infusion[3] Pharmacist-driven monitoring protocols have shown significant improvement in appropriate leucovorin dose escalations, highlighting the importance of careful monitoring during this therapy[8]. Since glucarpidase does not hydrolyze intracellular methotrexate, leucovorin rescue therapy remains important even after glucarpidase administration to protect cells from intracellular methotrexate toxicity[9].