What MTX level at 24 hours requires extended leucovorin?

MTX above 5 micromol/L at 24 hours indicates delayed clearance. MTX above 1 micromol/L at 48 hours and above 0.1 micromol/L at 72 hours requires continued or escalated leucovorin. Carboxypeptidase G2 (glucarpidase) is used for MTX above 10 micromol/L beyond 42 hours.

Why must leucovorin timing be precise?

Leucovorin competes with MTX for cellular uptake. Starting rescue too early may compromise antitumor efficacy; starting too late or giving insufficient doses allows ongoing MTX toxicity to mucosa, kidneys, and marrow. Standard rescue starts 24 hours after HDMTX infusion ends.

Methotrexate Leucovorin Rescue Interval

Determine leucovorin rescue timing and dose after high-dose methotrexate (HDMTX) based on serum MTX levels at 24, 48, and 72 hours using standard rescue nomograms.

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Frequently Asked Questions

What MTX level at 24 hours requires extended leucovorin?

Why must leucovorin timing be precise?