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Abstract: The management of patients who have developed a contact dermatitis due to topical drugs requires to stop the suspected drug application, to declare, if severe, the adverse drug reaction to a center for drug safety, to treat the patient with corticosteroid ointments, to perform dermatoallergological investigations e.g. drug patch tests in case of contact eczema and diluted prick tests in case of contact urticaria in order to determine whether the adverse drug reaction was due to excipients or to the drug itself. It is also absolutely necessary to advise the patient concerning the avoidance of topical but also systemic readministration of the responsible molecule. An excipient responsible in inducing a contact sensitization to a topical drug can also be found in cosmetics, the name of the responsible excipient has to be given to the patient under the common name but also under the INCI and/or CFTA name. When the drug itself is responsible in inducing a contact allergy it is necessary to determine if cross reactions with other drugs can occur and if the responsible molecule can induce systemic cutaneous adverse drug reactions if the drug is systemically readministred. Among NSAID there is no cross reactions between bufexamac and diclofenac, between salicylamide, glycol salicylate, salicylic acid and acetylsalicylic acid. In case of photosensitization 1) to ketoprofen or 2) piroxicam the topical and/or systemic administration of the following molecules are contraindicated with respectively 1) ketoprofen, tiaprofenic acid, fenofibrate, oxybenzone or 2) piroxicam, thimerosal. A patient sensitized to corticosteroid ointment has to be tested in order to determine which corticosteroid classes are sensitizing. The topical and systemic administrations of molecules belonging to the sensitizing classes (A, B, C, D1 or D2) have to be forbidden. In general, a contact dermatitis due to an antimicrobial drug induces a contraindication in further topical or systemic uses of the drug and to all the molecules belonging to the same class. In most of the cases there is no risk in systemically administering iodine, sulfites or excipients in a sensitized patient who had developed a contact dermatitis to topical medications. [Copyright &y& Elsevier]

The article presents a case report focusing on the diagnosis of allergic contact dermatitis to aciclovir. It is found that contact allergy to aciclovir appears to be rare and develops after recurrent use of the scartch-patch test. Scratch-patch testing should be considered when contact allergy to aciclovir is suspected and when conventional closed patch test shows negative results. Due to possible cross-reactions, the authors recommend testing an alternative topical antiviral drug before use.