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Related Experiment Video

Updated: Oct 3, 2025

Precision Implementation of Minimal Erythema Dose MED Testing to Assess Individual Variation in Human Inflammatory Response

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Delayed-type drug eruption to phenazopyridine (pyridium) confirmed with patch testing.

Winnie W Y Yeung¹, Christina S M Wong², Wai-Yan Leung¹

¹Division of Rheumatology & Clinical Immunology, Department of Medicine, Queen Mary Hospital, The University of Hong Kong, Hong Kong.

Asia Pacific Allergy

|February 17, 2022

Summary

Delayed hypersensitivity reactions are common with penicillin but rarely reported with Pyridium. This case highlights a patient experiencing a delayed hypersensitivity reaction to Pyridium, confirmed by skin patch testing.

Keywords:

Hypersensitivity Penicillin Phenazopyridine

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Last Updated: Oct 3, 2025

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Published on: October 3, 2019

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Published on: July 19, 2007

Area of Science:

Dermatology
Clinical Immunology
Pharmacovigilance

Background:

Delayed hypersensitivity reactions (DHR) are a known adverse effect of certain medications.
Penicillin-induced DHR is well-documented.
Phenazopyridine hydrochloride (Pyridium) is a urinary analgesic commonly used for symptomatic relief of urinary tract infections.

Observation:

A patient presented with a delayed hypersensitivity reaction following the use of Augmentin and Pyridium.
The patient's clinical presentation was suggestive of a DHR.

Findings:

Skin patch testing was performed to identify the causative agent.
Surprisingly, the patch test confirmed a delayed hypersensitivity reaction specifically to Pyridium.
This finding is novel as Pyridium-induced DHR has not been previously reported.

Implications:

This case expands the known spectrum of adverse drug reactions associated with Pyridium.
Healthcare providers should consider Pyridium as a potential cause of delayed hypersensitivity reactions.
Further investigation into the immunological mechanisms of Pyridium hypersensitivity may be warranted.