anaphylactic shock

n.
A sudden, severe allergic reaction characterized by a sharp drop in blood pressure, urticaria, and breathing difficulties that is caused by exposure to a foreign substance, such as a drug or bee venom, after a preliminary or sensitizing exposure. The reaction may be fatal if emergency treatment, including epinephrine injections, is not given immediately. Also called anaphylaxis.

An immediate over-reaction of the immune system following the administration of a drug or other agent (especially an allergen; see allergy), in an individual who has been previously exposed to the agent and who has produced antibodies against it. Anaphylactic shock is a potentially fatal form of hypersensitivity (see anaphylaxis). It is characterized by nausea, lowered blood pressure, irregular heart beats, vomiting, and difficulty in breathing due to a swelling of the larynx. It may lead to coma and death.

An immediate overreaction of the immune system to a drug or other agent in an individual who has previously encountered the agent and has produced antibodies to that agent. Anaphylactic shock is characterized by nausea, lowered blood pressure, irregular heart beat, vomiting, and difficult breathing. It may lead to coma or death. See also anaphylaxis.

An unusual or exaggerated allergic reaction of an animal to foreign protein or other substances. Anaphylaxis is an immediate or antibody-mediated hypersensitivity reaction (type I) produced by the release of vasoactive agents such as histamine and serotonin. Release is a consequence of the binding of IgE antibodies to Fc receptors on the surface of particularly mast cells and basophils. Antigen binding to two adjacent IgE molecules causes perturbation of the cell membrane leading to the release of vasoactive substances. Anaphylaxis may be localized, usually cutaneous, or generalized. Called also anaphylactic shock.
Substances most likely to produce anaphylaxis include drugs, particularly antibiotics and local anesthetics; drugs prepared from animals, such as insulin, adrenocorticotropic hormone and enzymes; diagnostic agents, such as iodinated x-ray contrast media; biologicals used to provide immunity, such as vaccines, antitoxins and gamma globulin; protein foods; the venom of bees, wasps and hornets; and pollens and molds. See also hypersensitivity, anaphylactic.

• acquired a. — that in which sensitization is known to have been produced by administration of a foreign antigen.
• active a. — see acquired anaphylaxis (above).
• aggregate a. — caused by large amounts of antibody–antigen complexes that activate complement and resulting in degranulation of mast cells.
• antiserum a. — passive anaphylaxis.
• cutaneous a. — a localized form of anaphylaxis, which follows the injection of antigen into the skin.
• cytotoxic a. — a form of anaphylaxis triggered by antibodies against self antigens. Blood transfusion reactions and Rh reactions are examples.
• cytotropic a. — refers to binding of IgE to Fc receptors.
• heterologous a. — passive anaphylaxis induced by transfer of serum from an animal of a different species.
• homologous a. — passive anaphylaxis induced by transfer of serum from an animal of the same species.
• indirect a. — that induced by an animal's own protein modified in some way.
• passive a. — that resulting in a normal animal from injection of serum of a sensitized animal.
• passive cutaneous a. (PCA) — localized anaphylaxis passively transferred by intradermal injection of an antibody and, after a latent period (about 24 to 72 hours), intravenous injection of the homologous antigen and Evans blue dye; blueing of the skin at the site of the intradermal injection is evidence of PCA.
• reverse passive cutaneous a. — antigen is injected first, succeeded by the injection of antiserum.
• systemic a. — a generalized anaphylactic reaction most often observed when the antigen is injected intravenously but may also be produced after local administration of antigen. The main shock organs in cattle and sheep are the lungs, in the horse, cat and pig the lungs and intestines, and in dogs the liver, specifically the hepatic veins.