The term anaphylaxis arose from the experiments of Richer and Portier in the early 1900s and meant the opposite of prophylaxis, i.e., a lack of protection rather than the expected immunity. Nevertheless, the reaction is indeed immune in nature and depends on the formation of IgE antibody, the immunoglobulin responsible for typical allergic reactions. The initial sensitization step induces the formation of IgE specifically directed to the initiating substance.
What is Anaphylactic rxn ?
In anaphylaxis, the reaction is systemic in nature, occurs rapidly after the administration of minute concentrations of the offending material, and is potentially fatal. How the allergen is given can dictate the manifestations and magnitude of the ensuing allergic reaction; although all routes can lead to anaphylaxis, parenteral administration is more likely than inhaled or ingested allergens to cause elevated circulating levels of unaltered allergen and a systemic reaction. Thus parenteral administration of medication and insect sting reactions (injected into cutaneous vessels) are among the most common causes of anaphylaxis.
What is Anaphylactoid rxn ?
Anaphylactoid reactions are defined as systemic reactions that have the same symptoms as anaphylaxis but are not due to an IgE-dependent mechanism and are not usually immune. Examples include reactions to radiographic contrast agents and non-steroidal anti-inflammatory drugs (e.g., acetylsalicylic acid, indomethacin, ibuprofen).