A 22-year-old woman comes to the emergency department after development of a diffuse pruritic rash following a meal at a buffet restaurant an hour ago. She also felt light-headed and nearly fainted. The patient has no prior medical conditions and takes no medications. Temperature is 37 C (98.6 F), blood pressure is 96/52 mm Hg, pulse is 126/min, and respirations are 16/min. Physical examination shows mild lip swelling; the tongue appears normal. Heart auscultation demonstrates regular tachycardia without extraneous sounds. Lung sounds are clear with normal work of breathing. Skin examination shows confluent urticaria on the neck, shoulders, and abdomen. Intravenous fluids are begun, and intramuscular epinephrine is administered immediately. In addition to its effect on airway and circulation, this medication is most likely to improve this patient's condition through which of the following mechanisms?

Question

A 22-year-old woman comes to the emergency department after development of a diffuse pruritic rash following a meal at a buffet restaurant an hour ago.  She also felt light-headed and nearly fainted.  The patient has no prior medical conditions and takes no medications.  Temperature is 37 C (98.6 F), blood pressure is 96/52 mm Hg, pulse is 126/min, and respirations are 16/min.  Physical examination shows mild lip swelling; the tongue appears normal.  Heart auscultation demonstrates regular tachycardia without extraneous sounds.  Lung sounds are clear with normal work of breathing.  Skin examination shows confluent urticaria on the neck, shoulders, and abdomen.  Intravenous fluids are begun, and intramuscular epinephrine is administered immediately.  In addition to its effect on airway and circulation, this medication is most likely to improve this patient's condition through which of the following mechanisms?

Quizplus · Accepted Answer

11ec160b_3b6d_68d5_9249_198eb44241b1_MD0001_00 This patient with sudden-onset rash and hypotension after ingesting a likely allergen has anaphylaxis. Anaphylaxis classically involves a type 1 (immediate) hypersensitivity reaction to an antigen, resulting in IgE-mediated mast cell and basophil degranulation. Sudden and massive release of inflammatory mediators (eg, histamine, leukotrienes) into the circulation can quickly lead to urticaria, oropharyngeal edema (eg, lip swelling), and shock (eg, hypotension, tachycardia). Epinephrine is the only pharmacologic therapy that both decreases the release of inflammatory mediators from mast cells and addresses all other manifestations of anaphylaxis. It binds to adrenergic receptors (eg, beta-2 receptors) on the surface of mast cells, inhibiting mast cell degranulation. In addition, it counteracts existing inflammatory effects via widespread stimulation of alpha- and beta-adrenergic receptors: Alpha-1: causes vasoconstriction and decreases vascular permeability, raising blood pressure and decreasing upper airway edema Beta-1: increases cardiac contractility and cardiac output, improving blood pressure and peripheral perfusion Beta-2: causes bronchodilation, relieving airflow obstruction Because of its ability to both treat and prevent further inflammatory mediator effects, epinephrine is the first-line treatment for anaphylaxis. (Choice A) H1 antagonists (eg, diphenhydramine) block tissue histamine receptors, preventing the effects of circulating histamine on capillaries (eg, vasodilation, increased vascular permeability). However, they do not decrease the mast cell release of histamine or other inflammatory mediators. (Choice B) Omalizumab is a monoclonal anti-IgE antibody that binds to free IgE at the same site where IgE normally binds to mast cell IgE Fc receptors. It prevents receptor binding and decreases circulating IgE levels, which eventually induces IgE Fc receptor down-regulation to help stabilize mast cells. (Choice C) Zileuton, a medication commonly used in the management of asthma, decreases the leukocyte synthesis of leukotrienes by inhibiting 5-lipoxygenase. This results in decreased leukotriene activity, reducing inflammation and bronchospasm. (Choice E) Glucocorticoids reduce inflammation by several mechanisms. One such mechanism is by promoting eosinophil apoptosis, either directly or by decreasing production of IL-5, which usually promotes eosinophil survival. This decreases the number of circulating eosinophils. Educational objective: Anaphylaxis is a type 1 (immediate) hypersensitivity reaction involving IgE-mediated mast cell and basophil degranulation. Epinephrine is the primary treatment for anaphylaxis because it decreases further mast cell release of inflammatory mediators and counteracts existing systemic inflammatory effects (eg, shock, bronchoconstriction). __________ References: Epinephrine: the drug of choice for anaphylaxis-a statement of the World Allergy Organization. (http://www.ncbi.nlm.nih.gov/pubmed/23282530)

A 22-Year-Old Woman Comes to the Emergency Department After Development