Usefulness of skin testing in cutaneous drug eruptions in routine practice

Background: Cutaneous drug eruptions are common side-effects. The imputation score combining intrinsic (chronology, clinical and paraclinical signs) and extrinsic criteria used in Pharmacovigilance Centres is insufficient alone to identify with certainty a responsible drug. Objective: To evaluate the imputation score before and after performing skin testing in patients with cutaneous drug eruptions. Patients/Methods: A single-centre retrospective study was performed on 339 patients tested between 2001–2006. Imputation scores were calculated before and after skin tests for each cutaneous drug eruption according to the clinical type of skin eruption and the type of drug. Results: Among 121 patients meeting inclusion criteria, 46% showed an increase of the imputation score as shown by 25/41 cases of maculo-papular exanthema, 4/11 cases of acute generalized exanthematous pustulosis and 17/41 cases of urticaria/anaphylaxis. The imputation score increased in 25/70 cases of the tested antibiotic drugs, in 14/56 cases of cardiovascular drugs, and it increased in 19 patients (34%) with I1 or I2 imputation scores before skin testing and in 29 (52%) with an I3 imputation score before skin testing. Conclusions: Drug skin testing appeared useful in investigating cutaneous drug eruptions in routine practice, including not only drugs with a high imputation score (I3) but also those with a lower score (I1, I2). Drug skin testing should lead to oral rechallenge of drugs with negative tests in order to determine which drugs may be used safely.