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Difficulty: EasyImmunologic and Inflammatory Processes

A 28-year-old woman is brought to the emergency department by ambulance due to the sudden onset of difficulty breathing, lip swelling, and a diffuse, intensely pruritic rash. The symptoms began approximately 15 minutes after she received her first dose of intravenous ceftriaxone for uncomplicated pyelonephritis at an urgent care clinic. Her temperature is 37.1°C (98.8°F), blood pressure is 78/45 mmHg, heart rate is 128/min, and respiratory rate is 26/min. Physical examination reveals stridor, diffuse expiratory wheezing, and bilateral angioedema of the face and lips. Which of the following mechanisms of action corresponds to the pharmacotherapy that must be administered immediately to stabilize this patient?

  1. Activation of alpha-1, beta-1, and beta-2 adrenergic receptorsAnswer
  2. B
    Competitive antagonism of peripheral H1-histamine receptors
  3. C
    Inhibition of phospholipase A2 to reduce arachidonic acid metabolites
  4. D
    Competitive antagonism of beta-1 and beta-2 adrenergic receptors
  5. E
    Blockade of leukotriene C4, D4, and E4 receptors

Answer

Activation of alpha-1, beta-1, and beta-2 adrenergic receptors represents the mechanism of epinephrine, which is the immediate, life-saving treatment required for anaphylaxis.
The patient is experiencing acute anaphylaxis, a severe, systemic Type I (IgE-mediated) hypersensitivity reaction. The absolute priority in management is immediate stabilization of the airway and cardiovascular system. Epinephrine is the required first-line therapy. Its alpha-1 adrenergic agonism causes vasoconstriction, which increases blood pressure and reduces mucosal edema (relieving upper airway obstruction). Its beta-2 adrenergic agonism induces bronchodilation and suppresses further mast cell degranulation. Its beta-1 agonism provides necessary inotropic support.

Step-by-Step Solution

1
Identify the clinical syndrome based on the patient's presentation.
The patient has acute respiratory compromise (stridor, wheezing), profound hypotension, and mucocutaneous signs (urticaria, angioedema) shortly after antibiotic administration. This is diagnostic for acute anaphylaxis (Type I hypersensitivity).
Rapid recognition of systemic anaphylaxis is crucial because delays in appropriate treatment significantly increase mortality.
2
Determine the most appropriate immediate pharmacotherapy and identify its mechanism of action.
Intramuscular epinephrine is the required first-line treatment. It acts as an agonist at alpha-1, beta-1, and beta-2 adrenergic receptors.
Alpha-1 agonism causes vasoconstriction to increase blood pressure and decrease upper airway mucosal edema. Beta-2 agonism causes bronchodilation and decreases further mast cell mediator release.

Key Concept

The immediate management of acute Type I hypersensitivity (anaphylaxis) requires intramuscular epinephrine, which acts via alpha and beta adrenergic agonism to reverse systemic vasodilation, vascular permeability, and bronchospasm.
Estimated Time:1m 0s
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Topics

Immunologic and Inflammatory Processes

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