[Skin tests in the study of drug eruptions with suspected immuno-allergic mechanism].

Skin testing (patch tests, prick test and intradermal tests) with the suspected compound has been reported to be helpful in determining the cause of cutaneous adverse drug reactions (ADRs), but the value and specificity of these tests need to be determined. In a previously published study involving 72 patients, we observed positive results in 72% of the cases, in 43%, 24% and 67% in patch, prick and intradermal skin tests, respectively. The results of skin tests varied with the clinical type of cutaneous ADR, as a significantly higher number of positive patch tests was observed in maculopapular rashes (59%) than in urticarial reactions (13%) or in eythrodermic ADR (80%). The results of patch tests varied with the drug tested as frequent positive results were obtained with amoxicillin, pristinamycin, carbamazepine, pseudoephedrine, heparinoids... This study and the analysis of the literature support the value of careful sequential drug skin testing in establishing the cause of cutaneous ADR. Guidelines are proposed for performing these tests, and these include the use of appropriate negative control patients to avoid false-positive results, the determination of the relevance of positive patch tests, a contact sensitization to drug being able to elicite a positive result on patch tests with a preserved oral tolerance to the same drug. These tests have to be performed with a strict medical survey as they can induce a relapse of the cutaneous ADR.