17.5: Allergic Reactions: Anaphylaxis

Anaphylaxis is a severe, life-threatening hypersensitivity reaction mediated by Immunoglobulin E (IgE) antibodies. When IgE binds to allergens, it triggers the release of mediators– histamine, leukotrienes, and prostaglandins from mast cells and basophils. These mediators cause vasodilation, edema, and inflammation, leading to various symptoms.

The primary allergens causing anaphylaxis include food items (e.g., peanuts, shellfish), drugs (e.g., penicillin, asparaginase, corticotropin, heparin), insect stings, and certain environmental substances (e.g., grass pollen, dust mites). Anaphylaxis can also result from exposure to radiological contrast agents, vaccines, and latex.

Anaphylaxis primarily affects the gastrointestinal tract, skin, respiratory, and cardiovascular systems. It leads to food allergies, urticaria, atopic dermatitis, rhinitis and asthma, and anaphylactic shock. Symptoms manifest quickly after exposure to the allergen and include urticarial rash, hives, swelling of soft tissues, angioedema, bronchoconstriction, wheezing, shortness of breath, and hypotension. If not treated promptly, these symptoms can rapidly progress into life-threatening conditions.

Anaphylactic shock is characterized by a sudden drop in blood pressure, respiratory distress, and potential cardiovascular collapse. Penicillin is responsible for about 75% of anaphylactic deaths due to its widespread use. Other drugs, local anesthetics, antiseptics, and contaminants in pharmaceutical preparations can also trigger anaphylaxis.

Diagnosing anaphylaxis involves skin tests for hypersensitivity, such as the prick or intradermal test, which can help identify the specific allergen triggering the reaction. Another method is detecting particular IgE in the plasma, which can confirm the presence of an allergic reaction. However, these tests are not routinely used and are usually reserved for cases where the cause of anaphylaxis is unclear. Immediate treatment includes the administration of epinephrine and supportive measures to manage symptoms and prevent severe outcomes.

Anaphylaxis is an immediate hypersensitivity reaction mediated by IgE antibodies. These antibodies bind to allergens, forming allergen–IgE antibody complexes. Common allergens include pollen, dust mites, drugs, and certain food items.

These complexes bind to receptors on mast cells and basophils, leading to rapid degranulation and the release of histamine, leukotrienes, and prostaglandins.

These mediators cause vasodilation, bronchoconstriction, edema, and neutrophil activation, generating an inflammatory response.

These reactions can severely affect the vasculature, GI tract, skin, and respiratory system. They may also manifest as conditions such as food allergies, urticaria, rhinitis, and asthma.

Various drugs can cause anaphylaxis, including penicillin, asparaginase, monoclonal antibodies, corticotropin, heparin, vaccines, local anesthetics, and antiseptics like chlorhexidine.

Diagnostic methods for anaphylaxis are clinical, based on symptoms. Skin tests, such as intradermal injection of penicilloylpolylysine can later identify penicillin allergy.