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Biphasic and protracted anaphylaxis

Phillip L Lieberman, MD
Section Editor
John M Kelso, MD
Deputy Editor
Anna M Feldweg, MD


Most episodes of anaphylaxis begin quickly, escalate, and then resolve completely, particularly when appropriate treatment is administered. However, some anaphylactic reactions resolve and recur hours later or do not resolve completely for hours or even days.

Atypical patterns of anaphylaxis, the incidence of atypical patterns of reactions, and proposed risk factors for these reactions will be reviewed here. The diagnosis and treatment of anaphylaxis, fatal anaphylaxis, and other topics related to anaphylaxis are discussed elsewhere. (See "Anaphylaxis: Emergency treatment" and "Fatal anaphylaxis" and "Differential diagnosis of anaphylaxis in children and adults".)


There are three recognized temporal patterns of anaphylaxis: uniphasic, biphasic, and protracted [1].

Uniphasic anaphylaxis — Uniphasic anaphylactic reactions are the most common type, accounting for an estimated 80 to 90 percent of all episodes. A uniphasic response usually peaks within 30 minutes to one hour after symptoms appear and resolves either spontaneously or with treatment within the next 30 minutes to one hour.

Protracted anaphylaxis — A protracted anaphylactic reaction lasts hours to days without clearly resolving completely. The exact frequency of protracted episodes of anaphylaxis is unknown, although they appear to be uncommon. The literature consists only of case reports and small series [2-6].

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Literature review current through: Dec 2017. | This topic last updated: Mar 31, 2016.
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