ABSTRACT
Anaphylaxis, literally “reversal of protection,” refers to an unpredictable, rapid, general-
ized, life-threatening reaction caused by exposure to an antigen to which the individual
had been previously sensitized (Box 1). Anaphylactoid reactions are clinically similar
but are not antigen-IgE mediated and do not require prior sensitization. Idiopathic
anaphylactic reactions occur without an identifiable pharmcologic or physical stimulus.
The more general term allergic reaction includes anaphylactic and anaphylactoid reac-
tions, as well as less dramatic, localized responses such as urticaria and isolated broncho-
spasm. The term “anaphylaxis” will be used generically in this chapter to encompass all
anaphylactic and anaphylactoid reactions, unless otherwise specified.
