Diagnostic approach to drug allergy.

The approach to drug hypersensitivity always comprises a clinical and a diagnostic workup. About 15% of drug side effects are due to hypersensitivity reactions. All types of immunological reactions can be induced by drugs, but type I and type IV reactions are seen most often. The initial judgment of the skin symptoms is therefore one of the key factors besides a stringent history of drug intake for a further diagnostic workup. The goal of a diagnostic workup is not only to identify the culprit drug, but also to defer the patient from similar drugs in order to prevent a second episode. In the case of missing alternatives and unidentified drug sensitivity, reexposure to the previous drug must be discussed; however, in severe cutaneous reactions this should generally be avoided.