# Loss of Tolerance in Long-Term Allergen Immunotherapy: A Case of Late-Onset Systemic Anaphylaxis

## TL;DR

A young man on long-term allergen immunotherapy experienced a severe allergic reaction, highlighting the need for continued monitoring and understanding drug interactions.

## Contribution

This case report identifies potential factors contributing to late-onset anaphylaxis during allergen immunotherapy.

## Key findings

- A patient on allergen immunotherapy for five years developed acute respiratory distress after a routine injection.
- Possible causes include loss of immune tolerance and interactions with concurrent fluoxetine treatment.
- The case underscores the importance of ongoing follow-up for patients on long-term allergen immunotherapy.

## Abstract

This case report documents a rare phenomenon of a serious systemic allergic reaction following nearly five years of ongoing allergen immunotherapy (AIT) in a 19-year-old male patient. The patient, stable on maintenance AIT for sensitization to dust mite, cat dander, and birch pollen, developed acute respiratory distress minutes after a routine injection. Emergency treatment with epinephrine, diphenhydramine, and salbutamol was successful. This case highlights several potential causes, including loss of immune tolerance, immune deviation due to infection, and possible immunomodulating properties of concurrent fluoxetine treatment. It is a reminder that patients on long-term AIT need to continue on follow-up and that drug-AIT interactions are an area for ongoing investigation.