Snapshot A 15-year-old male presents to the emergency room with dyspnea, wheezes, and urticaria. His symptoms developed approximately under an hour after eating at a restaurant. Medical history is significant for asthma and a severe allergic reaction to peanuts and shellfish. Airway, breathing, and circulation is intact. Patient is started on intramuscular epinephrine. Introduction A potentially life-threatening systemic allergic reaction can result in airway obstruction as well as cardiovascular collapse rapid onset (minutes to hours) Type I hypersensitivity reaction mast cell and basophil activation leads to inflammatory mediator release via IgE and non-IgE mediated mechanisms Causes foods (e.g., peanuts) insect stings/bites (e.g., bee stings) medications (e.g., sulfa-medications) Presentation Physical symptoms must include at least 2 organ systems skin and mucosa hives, itching, swelling of the conjunctiva, and swollen lips/tongue/uvula respiratory stridor, wheezes, and shortness of breath cardiovascular syncope hypotension tachycardia Evaluation Clinical diagnosis Differential Diagnosis Vasovagal syncope Diseases associated with flushing alcohol-induced rosacea carcinoid tumor Treatment Ensure airway, breathing, and circulation is intact Intramuscular (IM) epinephrine first-line therapy IM epinephrine is the preferred route of administration epinephrine mechanism of action α1 agonism results in increased vasoconstriction and decreases mucosal edema β1 agonism results in increased chronotropy and ionotropy β2 agonism results in bronchodilation and decreases inflammatory mediator release from mast cells and basophils Glucocorticoids and antihistamines have a slower onset of action should only be used as adjunctive therapy to epinephrine Prognosis, Prevention, and Complications Prevention avoid triggers patient education Complications airway obstruction and cardiovascular collapse Kounis syndrome allergic angina that can lead to acute coronary syndrome or myocardial infarction