Anaphylaxis

Anaphylaxis is a sudden, potentially life-threatening systemic hypersensitivity reaction that occurs rapidly after exposure to an allergen. It results from widespread mediator release from mast cells and basophils, leading to symptoms across multiple organ systems. The most common triggers are foods (such as peanuts, tree nuts, milk, eggs, shellfish), insect stings, medications (including beta-lactam antibiotics and NSAIDs), and, less commonly, exercise or unknown causes. Immunologic (IgE-mediated) reactions are typical, though non-IgE mechanisms can produce anaphylaxis.

Clinical presentation varies but usually involves more than one organ system. Skin signs such as hives, flushing, or swelling are common but not mandatory. Respiratory symptoms may include wheeze, shortness of breath, throat tightness, or hoarseness. Cardiovascular signs can include light-headedness, fainting, or shock. Abdominal symptoms such as vomiting may occur, and patients often report a sense of impending doom.

Diagnosis is clinical, based on the rapid onset after exposure and involvement of multiple organ systems. Serum tryptase can support the diagnosis if measured within one to two hours of onset but is not required. Later allergy testing may identify triggers, and supervised food challenges can help determine causation.

Treatment requires prompt administration of intramuscular epinephrine as soon as anaphylaxis is suspected. Dosing commonly is 0.3–0.5 mg for adults and 0.01 mg/kg up to 0.3 mg for children, injected into the mid-outer thigh. If symptoms persist or recur, a second dose may be given after several minutes. Call emergency services, and provide airway support, oxygen, and intravenous fluids as needed. Antihistamines and corticosteroids may be used as adjuncts but are not substitutes for epinephrine. After stabilization, observation for several hours is typical due to the possibility of biphasic reactions.

Prevention focuses on trigger avoidance, carrying an epinephrine auto-injector, and developing an action plan. Education and follow-up with an allergy specialist are advised.