Delayed renal excretion of methotrexate after a severe anaphylactic reaction to methotrexate in a child with osteosarcoma.

Although methotrexate is an agent widely used in the practice of pediatric oncology, allergic reactions to methotrexate are most unusual. Most of these reactions typically occur after repeated administration. Here, we report a severe anaphylactoid reaction to the first dose of high-dose methotrexate infusion in a child with osteosarcoma who has also experienced a delayed excretion of methotrexate. Clinicians must be aware of the possibility of a systemic, near-fatal anaphylactic reactions with methotrexate and patients who experience severe anaphylactic reactions should be followed carefully because of the possibility of delayed methotrexate excretion.