Anaphylactoid reaction to high-dose methotrexate and successful desensitization.

Anaphylactic/anaphylactoid reaction to methotrexate (MTX) is uncommon. It may occur with the first dose (non-allergic reactions) or after a previous exposure to the drug (allergic or specific reactions). Desensitization has been shown effective in children with allergic-type reactions permitting the continuation of high-dose methotrexate (HDMTX) therapy. We report the case of a child with localized osteosarcoma who developed an anaphylactoid reaction after a first HDMTX course. A desensitization protocol was successfully applied allowing the administration of four additional courses. In our experience, desensitization can be a safe and effective procedure in children with anaphylactoid reactions to HDMTX.