Anaphylactoid reaction to high-dose methotrexate and re-administration after a successful desensitization.

Methotrexate (MTX) is an antimetabolite with a major role in the treatment of acute lymphoblastic leukaemia (ALL). The authors report the management of a 9-year-old boy who developed an anaphylactoid reaction to high-dose MTX infusion, after a first challenge with intrathecal administration, during induction therapy for ALL. A desensitization protocol was followed and MTX tolerance has been successfully achieved, allowing this patient to complete the needed chemotherapy.