Cutaneous allergic drug reactions: update on pathophysiology, diagnostic procedures and differential diagnosic.

Important changes in the understanding and management of drug hypersensitivity reactions during the last years result from the increasing importance of biologics in medical practice, which differ in their spectrum of adverse drug reactions (ADRs) from the classical covalent drugs. With regard to covalent drugs, ampicillin and amoxicillin as well as clavulanic acid play an increasing role among ADRs to betalactam antibiotics. Fluoroquinolones are mainly the cause of anaphylactic and photosensitivity reactions. Especially in allergic reactions to NSAIDs, pseudoallergic reactions should be considered in the differential diagnosis. In opposite to the main cutaneous allergic drug reactions such as urticaria or maculopapular skin rash, in which antibiotics are the main culprits, in severe drug allergic reactions such as SJS (Stevens-Johnson Syndrome), TEN (Toxic Epidermal Necrolysis), or DRESS (Drug Reaction with Eosinophilia and Systemic Symptoms) Syndrome, compounds like allopurinol and anticonvulsants are the main causes. Similar mutations in the IL36R gene, which were found in both patients with an AGEP (Acute Generalized Exanthematous Pustulosis) and pustular psoriasis, make the differential diagnosis more difficult and raise the question whether there is a difference between these diseases or whether AGEP is not just a drug induced pustular psoriasis. Finally, some special aspects of side effects of biologics and targeted therapies respectively are discussed.