Half-dose glucarpidase as efficient rescue for toxic methotrexate levels in patients with acute kidney injury

Purpose High-dose methotrexate (HDMTX)-associated acute kidney injury with delayed MTX clearance has been linked to an excess in MTX-induced toxicities. Glucarpidase is a recombinant enzyme that rapidly hydrolyzes MTX into non-toxic metabolites. The recommended dose of glucarpidase is 50 U/kg, which has never been formally established in a dose finding study in humans. Few case reports, mostly in children, suggest that lower doses of glucarpidase might be equally effective in lowering MTX levels. Methods Seven patients with toxic MTX plasma concentrations following HDMTX therapy were treated with half-dose glucarpidase (mean 25 U/kg, range 17–32 U/kg). MTX levels were measured immunologically as well as by liquid chromatography–mass spectrometry (LC–MS). Toxicities were assessed according to National Cancer Institute—Common Terminology Criteria for Adverse Events (CTCAE) v5.0. Results All patients experienced HDMTX-associated kidney injury (median increase in creatinine levels within 48 h after HDMTX initiation compared to baseline of 251%, range 80–455%) and showed toxic MTX plasma concentrations (range 3.1–182.4 µmol/L) before glucarpidase injection. The drug was administered 42–70 h after HDMTX initiation. Within one day after glucarpidase injection, MTX plasma concentrations decreased by ≥ 97.7% translating into levels of 0.02–2.03 µmol/L. MTX rebound was detected in plasma 42–73 h after glucarpidase initiation, but concentrations remained consistent at < 10 µmol/L. Conclusion Half-dose glucarpidase seems to be effective in lowering MTX levels to concentrations manageable with continued intensified folinic acid rescue.