Leucovorin Rescue in Cancer Treatment

Introduction to Leucovorin Rescue

Leucovorin rescue is a life-saving antidote strategy that provides reduced folates to bypass methotrexate's toxic blockade of dihydrofolate reductase in normal cells, allowing DNA synthesis to resume while maintaining antitumor effects, and must be initiated within 24 hours of high-dose methotrexate administration to prevent potentially fatal toxicity, as recommended by the American College of Medical Toxicology 1, 2

Leucovorin is most effective when initiated within hours of the last methotrexate dose, with efficacy decreasing dramatically over time and becoming doubtful if started later than 24 hours after methotrexate administration, according to the American Society of Clinical Oncology 3
In cases of inadvertent overdose or delayed excretion, leucovorin rescue should begin as soon as possible and within 24 hours of methotrexate administration, as per the National Comprehensive Cancer Network guidelines 3
The standard dose of leucovorin is 15 mg (10 mg/m²) administered IV, IM, or PO every 6 hours until serum methotrexate level falls below 10⁻⁸ M, as recommended by the European Society for Medical Oncology 3

Hydration with 3 L/day or 125 mL/m²/hr IV is essential in leucovorin rescue, as recommended by the American College of Emergency Physicians 1
Urinary alkalinization to maintain urine pH ≥7.0 using sodium bicarbonate is crucial until methotrexate level <0.05 micromolar, according to the American Society of Health-System Pharmacists 1
Monitoring of serum creatinine and methotrexate levels at least once daily is necessary, with more frequent monitoring in complicated cases, as per the National Institute for Occupational Safety and Health guidelines 1

For patients with gastrointestinal toxicity, nausea, or vomiting, leucovorin must be administered parenterally rather than orally, as recommended by the American Gastroenterological Association 1
G-CSF (filgrastim) 5 mcg/kg/day subcutaneously is recommended for toxic bone marrow suppression, according to the American Society of Clinical Oncology 1, 3
Activated charcoal is indicated if ≥1 mg/kg methotrexate ingested within 1 hour, as per the American Association of Poison Control Centers 1, 3
Hospital admission is required for monitoring and sepsis surveillance due to high mortality risk, as recommended by the Society of Critical Care Medicine 1, 3

For low-risk gestational trophoblastic neoplasia, leucovorin 15 mg orally 30 hours after each methotrexate injection is recommended, as per the American College of Obstetricians and Gynecologists 1
For high-risk gestational trophoblastic neoplasia, leucovorin 15 mg IV/PO every 12 hours for 4 doses, starting 24 hours after methotrexate infusion, is recommended, according to the European Society for Medical Oncology 1
For acute lymphoblastic leukemia, leucovorin 10 mg/m² starting at 42 hours, repeated every 6 hours for 3 doses, is recommended, as per the American Society of Clinical Oncology 1
For osteosarcoma, high-dose methotrexate with leucovorin rescue is standard, though exact contribution to efficacy remains debated, according to the European Musculo-Skeletal Oncology Society 4

MTHFR genotyping is recommended for patients requiring additional cycles after prolonged high methotrexate levels to identify those at increased toxicity risk, as per the American College of Medical Genetics and Genomics 2