Usefulness of Cutaneous Provocation Tests to Study Drugs Responsible for Cutaneous Adverse Drug Reactions

Abstract

Cutaneous adverse drug reactions, particularly immune-mediated idiosyncratic reactions, are a very challenging area of Dermatology. For confirming the culprit drug, after a complete history of drug exposure with its chronologic relation with the eruption and characterization of the pattern of the drug eruption, skin provocation tests can be performed after resolution of the acute phase. Patch tests are indicated in the study of non-immediate T cell–mediated drug eruptions (maculopapular exanthema, drug reaction with eosinophilia and systemic symptoms (DRESS), Stevens–Johnson syndrome (SJS)/toxic epidermal necrolysis (TEN), acute generalized exanthematous pustulosis, fixed drug eruption, and drug photoallergy). It is recommended to test with pure drugs usually at 10% pet commercialized as patch test allergens, but in most cases, drugs have to be prepared in house, whenever possible in a final dilution at 10% pet. Methods are similar to patch testing in allergic contact dermatitis except in fixed drug eruptions where duplicate tests are needed; one of them applied for 24 h on a residual lesion. Patch tests are safe and highly specific when performed according to the recommendations, but sensitivity is highest in exanthemas, DRESS, and fixed drug eruptions and particularly for abacavir, carbamazepine, aminopenicillins and other antibiotics, diltiazem, and tetrazepam. Allopurinol is never positive, and reactivity is low in SJS/TEN. Therefore, a negative patch test cannot exclude a possible culprit, but a positive patch test is almost always relevant. Patch tests with drugs are also useful for evaluating cross-reactions and studying effector mechanism involved in the cutaneous adverse reaction.