# Anaphylaxis to Oral Trimethoprim-Sulfamethoxazole in a Child: A Case Report

## TL;DR

A child had a severe allergic reaction to a common antibiotic, showing that new testing methods may be safer for diagnosing drug allergies.

## Contribution

This case report introduces basophil activation testing as a potential safer diagnostic tool for TMP-SMX allergy.

## Key findings

- A six-year-old girl experienced anaphylaxis after taking trimethoprim-sulfamethoxazole.
- Basophil activation testing confirmed allergy to TMP-SMX despite a negative skin prick test.
- BAT may offer a safer alternative to drug provocation tests for diagnosing this allergy.

## Abstract

Trimethoprim-sulfamethoxazole (TMP-SMX) is a non-β-lactam antibiotic commonly used in pediatrics to treat infections and as a prophylactic medication. Hypersensitivity to TMP-SMX is generally non-immediate, and immediate allergic reactions, including anaphylaxis, are rare. This case report details a six-year-old girl who experienced anaphylaxis to TMP-SMX. Her skin prick test with TMP-SMX was negative, but she developed anaphylaxis in a drug provocation test (DPT). An additional basophil activation test (BAT) for the TMP-SMX combination tablet was evaluated and was confirmed positive. This case underscores the need for alternative diagnostic methods like BAT, which pose a lower risk than DPT. The findings suggest that BAT could offer a safer diagnostic approach, though more studies are required to validate its use for TMP-SMX allergy diagnosis.