Pathophysiology of Allergic Drug Reactions.

Adverse drug reactions (ADR) may be broadly divided into types A and B. Type A comprise the majority of reactions, can affect any individual, and are predictable from the known pharmacologic properties of a drug. Type B are less common, occur in susceptible patients and cannot be predicted. Allergic/immunologic drug reactions are a group of type B ADRs. Based on the time of onset allergic drug reactions can be divided into immediate and delayed and based on their underlaying immunologic mechanism, they can be further subdivided into 4 groups: immediate and mediated by IgE (1), delayed and caused by antibody facilitated cell destruction (2), delayed and caused by drug immune complex deposition and complement activation (3) and delayed and T cell mediated (4). Physicians should always insist on obtaining a thorough patient's history regarding drug allergy as well as on ascertaining details regarding the medication used, its route of administration, dosage and the treatment duration in order to properly assess risk of drug allergies and suggest further work-up in that regard.