Background and objectives: Based on previous studies revealing acid-suppression medication as a risk factor for food allergy tolerance induction, we aimed to establish the importance of those findings in patients undergoing oral immunotherapy (OIT).Materials and methods, results: We describe a case series of four patients who underwent milk OIT with a concomitant use of proton pump inhibitor (PPI) medication and who developed anaphylaxis after a known, previously tolerated dose of milk.Conclusions: PPIs may act as a cofactor in patients undergoing OIT, triggering adverse reac-tions, irrespective of the PPI used or the dosage. It would be necessary to separate the admin-istration of drug from food intake.Since OIT is a new form of treatment, long-term adverse events arising from PPI treatment and other possible triggers are still uncertain. Consequently, monitoring of patient must be prolonged over time. Additional investigations on the influence of different drugs in OIT main-tenance phase are required.

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