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How does histamine contribute to anaphylaxis after an insect sting?
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antihistamine
Antihistamines such as Benadryl (diphenhydramine) and Claritin (loratadine) can be purchased without prescriptions. Both of those agents act by blocking H1 receptors. However, whereas Benadryl binds to those receptors in the central nervous system (CNS), causing drowsiness, Claritin does not readily enter the CNS and thus does not normally cause drowsiness.
In the context of an insect sting, anaphylaxis is a severe, systemic allergic reaction triggered when the body’s immune system recognizes the insect venom as a threat.1
When a sensitized individual is stung, antibodies of the immunoglobulin E (IgE) class, which are bound to mast cells and basophils, bind to the venom antigens. This interaction stimulates these cells to undergo degranulation, releasing large amounts of inflammatory chemicals, most notably histamine.123
Once released, histamine contributes to anaphylaxis through several systemic effects:12
- Smooth muscle contraction: It causes the muscles in the bronchi to constrict, leading to significant difficulty in breathing.14
- Vascular changes: It causes the dilation of blood vessels and increases their permeability. This allows fluid to leak from the bloodstream into tissues, resulting in swelling (edema), skin flushing, hives, and a dangerous, abrupt drop in blood pressure.124
Because these reactions can be life-threatening, immediate treatment with epinephrine is required to reverse these effects.1