D1.95 - Utility and safety of Patch Testing in anti-epileptic Induced DRESS: Diagnostic sensitivity and cross-reactivity profiling

Drug Rash with Eosinophilia and Systemic Symptoms (DRESS) is a rare but potentially lifethreatening hypersensitivity reaction. Aromatic anti-epileptics (AEs) such as carbamazepine, phenytoin, and phenobarbital are among the most frequently implicated drugs. In this context, skin patch testing (PT) has emerged as a crucial tool, not only for confirming the causative drug but also for assessing cross-reactivity between different AEs and guiding the safe selection of alternative therapies. This study aims to evaluate the utility and safety of patch tests in case serial patients with AE-induced DRESS.

Cases of AE-induced DRESS and explored by patch testing, reported to the Pharmacovigilance center of Sousse were included in our study. The period of the study was of 5 years between January 2020 to December 2025. Patch tests were performed at least six weeks after the acute phase, using the commercial formulations of the suspected AEs and alternative AEs. 

Seventeen patients (male-to-female ratio 1.4; mean age 42 years) were included. Patch tests were positive in 15 patients (88.2%), demonstrating excellent sensitivity (100%) for valproic acid and phenytoin, and very high for carbamazepine (91.6%).Cross-reactivity between different AEs was demonstrated in two patients (11.8%): one case between phenytoin and phenobarbital (both aromatic AEs), and a second, more atypical case between levetiracetam (a non-aromatic AE) and valproic acid.  The negative results for alternative AEs allowed clinicians to prescribe tested AEs without recurrence of DRESS, avoiding the need for potentially less effective or more costly options. No adverse local or systemic reactions related to the patch testing were reported.

Our study confirms that patch testing, performed according to current standards, is an essential and safe tool in the long-term management strategy for AEs-induced DRESS. Beyond its high diagnostic sensitivity for the main AEs, it allows for the mapping of a patient's cross-reactivity profile.