394 Desensitization Protocol to Methotrexate

BACKGROUND: A 17 year old patient was referred to Allergy outpatient clinic with history of recent anaphylaxis (wheezing, breathlessness, nausea, vomit and hypotension) to methotrexate (MTX) during the induction treatment of ALL L2. The diagnostic confirmation consisted in a skin test, with a positive response at 1:100 dilution. The case was discussed together with Pediatric Oncology service, and was agreed that MTX was necessary for the patient survival, because of that we performed the following desensitization protocol. OBJECTIVE: Evaluate the effect and safety of a desensitization protocol to methotrexate in an adolescent with acute lymphoblastic leukemia L2 (ALL L2) and allergy to methotrexate. METHODS: Desensitization protocol consisted in 2 phases. First phase consisted in premedication with hydrocortisone (IV) 1 mgkgdo, cetirizine (PO) 0.2 mgkgdo, chlorpheniramine (IV) 0.35 mgkgdo and montelukast (PO) 10 mgdo at 13, 7 and 1 hour prior to desensitization phase which consisted in an 8 hour scheme of IV infusion of 12 dilutions with increasing concentrations starting at 1:1,000,000 at 30 minutes intervals up to the full dose was completed. RESULTS: Patient was admitted to pediatric intensive care unit and was successfully desensitized, the full protocol was completed as expected, including pre-medication, the desensitization phase lasted 8 hours; at the second dilution (1:100,000) the patient presented nausea, requiring one extra dose of chlorpheniramine, no other adverse reactions were presented in the next 48 hours observation period. He was maintained with 50 mg/m(2) IV MTX weekly for the full anti-leukemia treatment duration (1–2 years) using the same protocol and stayed out of MTX-related adverse reactions. Today he is followed as an outpatient by our service. CONCLUSIONS: This 12 steps MTX-desensitization protocol was effective and safe. In selected cases of severe allergic reactions to chemotherapeutic agents there where no other equally effective treatment option available, desensitization is effective and safe.