Pseudo-allergic reactions to drugs and chemicals.

Drugs can interfere with the immune system in two basically different ways: (1) they may interact with the specific recognition mechanisms of the immune system and thus induce an allergic response that is specific for the offending agent; (2) drugs may exert pharmacological effects on the immune systems which result in a response that is independent of its recognition structures or they may activate effector and amplification mechanisms that are normally triggered by specific immune processes. Allergic reactions to drugs are different from reactions that exhibit the same clinical symptoms but lack the specificity of an allergic reaction to the offending agent. It has been suggested that those non-specific reactions which mimic the signs and symptoms of allergic reactions should be classified as pseudo-allergic reactions (PAR). PAR are characterized by the following properties which differentiate them from allergic reactions. (1) The symptoms of PAR are qualitatively different from the pharmacological response of a drug and are not related to adverse reactions connected with its pharmacological and toxicological profile. (2) PAR are not specific with regard to the chemical structure of the triggering agent. (3) PAR lack transferability to other subjects of the same species. (4) In contrast to the allergic reactivity, the pseudo-allergic reactivity is not acquired but genetically predetermined. (5) Pseudo-allergic reactivity is often expressed upon the first contact with an eliciting agent. PAR are thus an expression of a pharmacological interaction of drugs or their metabolites in genetically predisposed individuals.