[Results of skin tests to assess drug-induced allergy].

Background: Skin tests are often used to explore adverse drug reactions. The sensitivity of skin tests appears to vary according to the drugs tested and the type of adverse reaction in question. There is no clear strategy to explore drug adverse reactions. The aim of this study was to determine the frequency of positive results for the different skin tests according to therapeutic class tested and type of adverse reaction. The secondary objective was to study response to the test drugs at different dilutions.

Patients And Methods: We retrospectively selected all patients presenting a suspected adverse drug reaction investigated in our clinic by patch test (PT), prick test (pt) and intradermal test (IDT). The suspected drugs and a pre-established list of substances from the same therapeutic family were systematically tested. Medical records from patients with Lyell syndrome, fixed drug eruption, photosensitivity and Drug Eruption with Eosinophilia and Systemic Symptoms (DRESS) syndrome were excluded. Adverse drug reactions were divided into two groups: the U group (urticaria or angioedema) and the E group (maculopapular-rash, erythroderma and generalized eczema).

Results: Four hundred and twenty-nine adverse drug reactions in 319 patients were assessed: 200 in the U group and 229 in the E group. In total, 61.8% presented at least one positive test for the suspected therapeutic class: 67.5% in the U group and 56.8% in the E group. In the U group, patch tests were positive in 14% of cases for betalactams, 17% for NSAIDs and 6% for radio-contrast media (RCM); in the E group, PT were positive in 12% of cases for betalactams, 9% for NSAIDs and 2% for RCM. Prick-tests were positive in the U group in 73% of the betalactams explored, 40% for the NSAIDs and 40% for the RCM; in the E group, pt were positive in 51% for betalactams, 32 for NSAIDs and 35% for RCM. IDT were positive in the U group in 13% for betalactams, 10% for NSAIDs and 40% for RCM; in the E group, IDT were positive in 14% for betalactams, 7% for NSAIDs and 40% for RCM. In the U group, pt were positive in 50% of cases with a diluted aliquot and in 48% of cases for IDT; in the E group pt were positive in 3% of cases with a diluted aliquot and in 63% of cases for IDT. The main limitations of this study are due to its retrospective nature and to the absence of evaluation of the specificity and relevance of the positive tests.

Conclusion: In patients presenting adverse drug reactions such as urticaria, angioedema, maculopapular rash, erythroderma and generalized eczema, the frequency of positive tests is high in general and for each therapeutic class (betalactams, NSAIDs, RCM). Diluted aliquots for pt remained sensitive and could be useful in exploring urticaria or angioedema, in the same way as diluted aliquots for IDT in both types of reaction. Better standardization of test procedures (including diluted aliquots) and of result reading would improve evaluation of the specificity and relevance of skin tests in adverse drug reactions.