Anaphylaxis is a life threatening condition that is brought about by a severe allergic reaction.

Mechanism of anaphylaxis

The triggers or causes of anaphylaxis may range from insect venom or stings to foods, drugs and medications. The trigger may be exercising in cold dry climates as well.

Most of these triggers however act via Immunoglobulin E (IgE). The IgE cross links with the mast cells and basophils binding to FceRI present on these cells.

Once bound this gives rise to a chain of reactions where the complement and coagulation systems are activated and T-cells are activated along with release of neuropeptide (substance P) release and cytotoxicity.

There is activation of phospholipase A2, Cycloxygenases (COXs), and lipooxygenases that lead to production of arachidonic acid metabolites like prostaglandins and leukotrienes and platelet-activating factor (PAF).

In addition interleukins like IL-6, IL-33 and TNF-a (Tumor necrosis factor alpha) are also released as late reactants.

The process of autoimmunity may also be triggered. While the immune system normally attacks invaders, mediators of autoimmunity fail to distinguish between self and foreign and tend to attack the body’s own tissues.

Exercise or exposure to cold air or cold water can also lead to anaphylaxis. These occur by non-immune reactions and activations of mast cells and basophils. Thus these reactions are not IgE mediated.

Biphasic type of anaphylaxis

Anaphylactic reactions may range in severity from mild to life threatening. The initial acute reaction is acute and active anaphylaxis. Adrenaline is the first line of treatment in these cases.

Other supportive measures include removal of the trigger (e.g. bee sting), oxygen and fluids along with antihistamine agents and steroids to curb the inflammation.

Most cases respond promptly to initial management. In some cases the reactions may last 24 hours or more despite medical treatment.

In some cases the symptoms and signs may resolve completely on initial therapy only to return later. The second time around the reactions may be more severe and may be life-threatening. The interval between the attacks may be between 2 and 72 hours (an average of 6 to 10 hours).

Some reported studies suggest the biphasic reactions for around 18 to 23% of all anaphylaxis reactions. It has been suggested that those who ingest the antigen, for example one with a peanut allergy consuming the same, are more at risk of a biphasic response.

Biphasic response also typically requires more adrenaline to be treated. Patients who require more adrenaline to curb initial symptoms are thus likely to suffer a biphasic response and need to be kept hospitalized for over 24 hours under observation.

Further Reading

• All Anaphylaxis Content
• Anaphylaxis – What is Anaphylaxis?
• Anaphylaxis Causes
• Anaphylaxis Treatment
• Anaphylaxis Prevention

Written by

Dr. Ananya Mandal

Dr. Ananya Mandal is a doctor by profession, lecturer by vocation and a medical writer by passion. She specialized in Clinical Pharmacology after her bachelor's (MBBS). For her, health communication is not just writing complicated reviews for professionals but making medical knowledge understandable and available to the general public as well.