Cutaneous adverse drug reactions: enhanced imputation score by skin testing

Introduction. A careful diagnosis and the identification of the causative d rug after a cutaneous adverse reaction can avoid relapses. Skin tests facil itate the identification of the causative molecule by producing a hypersens itivity reaction at the application site. Adverse drug reactions are report ed to Pharmacovigilance Centres who determine the imputation score of the s uspected drugs. The aim of this study was to assess to what extent skin tes ting after a suspected allergic drug reaction can be helpful to identify th e causative drug and whether an im pact on the final imputation score could be evidenced. Method. A 18-month prospective study was performed. All patients with a his tory of cutaneous adverse drug reaction of suspected immunoallergic origin were included provided skin tests could be performed within 6 to 12 weeks a fter the adverse drug reaction. The imputation score was determined using t he French imputation method prior to and after skin testing. Results. Thirthy-nine patients were included in the study. Positive skin te sts were observed in 11 of 20 patients with a C2S2 (12: plausible) initial imputation score and in 6 of 15 patients with a C2S1 (11: doubtful) initial imputation score. One patient with a C1S1 [11: doubtful) initial imputatio n score had positive skin tests. Discussion. The results of skin tests helped change the imputation score of the suspected drug in 18 patients out of 39 In 55 p. too of cases, the imp utation score was increased from C2S2 [12) to C2S3 (13: likely) and from C2 S1 (11) to C2S3 (13) in 40 p. 100 of cases. The increase in imputation scor es was helpful to improve warning signals after an immunoallergic reaction. Skin tests led to a more accurate diagnosis in 50 p. 100 of cases. Thus, m ore adequate advices for further drug treatment were possible, particularly in avoiding the irrelevant prohibition of innocent drugs.