3. Drug hypersensitivity.

Most drug reactions are pharmacological reactions rather than hypersensitivity reactions. In assessing drug reactions, a detailed clinical history and careful documentation of reactions are most important. Elucidating the nature and time course (first versus subsequent exposure, immediate versus non-immediate) of a reaction can help to distinguish immune from non-immune hypersensitivity, as well as IgE-mediated from T cell-mediated allergy. Skin testing and in-vitro tests are of predictive value for only a limited group of IgE-mediated drug allergic reactions. Drug provocation challenges can be used to eliminate suspicion of a low-probability drug reaction, find a safe alternative to a proven or probable drug reaction, or as a means of desensitisation. If a patient taking an angiotensin-converting enzyme (ACE) inhibitor develops angioedema, the cause must be assumed to be the ACE inhibitor until proven otherwise.