The Role of Patch Testing in Evaluating Delayed Hypersensitivity Reactions to Medications

Area of Science:

• Dermatology
• Pharmacology
• Immunology

Background:

• Confirming drug imputability is crucial for managing cutaneous adverse drug reactions (CADR).
• Drug re-challenge is often inconvenient and potentially life-threatening.
• Patch testing is a valuable diagnostic tool for identifying causative agents in CADR.

Purpose of the Study:

• To review literature on optimal patch testing techniques for specific CADRs.
• To provide an overview of expert recommendations and evidence on patch testing utility.
• To identify common CADRs and specific drugs/classes where patch testing is beneficial.

Main Methods:

• Literature review of patch testing techniques for CADRs.
• Testing performed approximately 3 months post-eruption resolution.
• Use of standard patch testing with drug preparations, excipients, and adjusted immunosuppressants.

Main Results:

• Patch test positivity varies significantly based on drug properties and CADR type.
• High positivity rates observed for beta-lactam antibiotics, aromatic anticonvulsants, phenytoin, and corticosteroids.
• Patch testing is potentially worthwhile for morbilliform eruptions, fixed drug eruption, AGEP, hypersensitivity syndrome, photoallergic, and eczematous reactions.

Conclusions:

• Patch testing is a valuable method for diagnosing specific CADRs, particularly morbilliform eruptions and fixed drug eruptions.
• Utility varies by drug and reaction type; not recommended for severe CADRs like SJS/TEN or leukocytoclastic vasculitis.
• Optimal testing involves specific timing, drug concentrations, excipient testing, and managing immunosuppressive therapy.