Hypersensitivity reaction to high-dose methotrexate and successful rechallenge in a pediatric patient with osteosarcoma.

Hypersensitivity reactions to methotrexate are rare, but have been reported. Methotrexate has shown activity against many malignancies, and omission of methotrexate therapy may increase the risk of cancer-related death in some patients. Therefore, rechallenging patients with methotrexate following hypersensitivity may be beneficial. We report a case of a child with metastatic osteosarcoma who experienced a hypersensitivity reaction to high-dose methotrexate and was successfully rechallenged with methotrexate using a 6-hour infusion. Using this regimen, adequate peak methotrexate plasma concentrations were achieved and no further hypersensitivity reactions were noted.