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Difficulty: EasyPharmacologic Interventions

A 35-year-old woman is brought to the emergency department immediately after accidentally ingesting a meal containing peanuts. She is in marked respiratory distress with audible stridor and diffuse urticaria. Her blood pressure is 75/40 mm Hg, heart rate is 135/min, and oxygen saturation is 91% on room air. Arrange the following pharmacologic interventions in the correct sequence of prioritization for the initial stabilization of this patient, from the most immediate life-saving intervention to adjunctive therapy.

  1. 1Intramuscular epinephrine (0.3 mg)
  2. 2Rapid intravenous infusion of 0.9% normal saline
  3. 3Intravenous diphenhydramine
  4. 4Intravenous methylprednisolone

Answer

The correct sequence is: Intramuscular epinephrine, followed by Intravenous normal saline, then Intravenous diphenhydramine, and finally Intravenous methylprednisolone.
The correct prioritization of pharmacologic interventions in anaphylactic shock requires addressing the most immediate life-threatening physiological derangements first. Intramuscular epinephrine rapidly reverses vasodilation and airway edema, making it the absolute first step. Following this, intravascular volume must be repleted with crystalloid fluids to manage distributive shock. Only after these stabilizing measures should adjunctive therapies like antihistamines (for hives) and corticosteroids (to prevent biphasic reactions) be administered, as these do not treat the acute life threats.

Step-by-Step Solution

1
Identify the primary diagnosis and immediate life threat.
The patient is experiencing severe anaphylactic shock with impending airway compromise (stridor) and cardiovascular collapse (hypotension).
Recognizing the severity of the allergic reaction dictates the urgency and choice of initial pharmacologic therapy.
2
Select the first-line pharmacologic intervention.
Prioritize intramuscular epinephrine.
Epinephrine's alpha-1 and beta-2 adrenergic effects immediately counteract vasodilation, bronchoconstriction, and mucosal edema. It is the only medication proven to reduce mortality in anaphylaxis.
3
Address the patient's severe hypotension.
Administer rapid intravenous crystalloid fluids (0.9% normal saline).
Anaphylaxis causes profound distributive shock due to increased vascular permeability. Large volume fluid resuscitation is necessary after or alongside epinephrine administration to restore intravascular volume.
4
Select immediate adjunctive medications for symptom relief.
Administer intravenous diphenhydramine.
H1-antihistamines act rapidly to block peripheral histamine receptors, providing symptomatic relief for urticaria and pruritus, though they do not reverse shock or airway obstruction.
5
Select delayed adjunctive medications to prevent recurrence.
Administer intravenous methylprednisolone.
Systemic corticosteroids reduce underlying inflammation and help prevent biphasic anaphylaxis, but because their onset of action takes 4 to 6 hours, they are prioritized last in the acute sequence.

Key Concept

In the management of severe anaphylaxis, intramuscular epinephrine is the undisputed first-line therapy and must be given prior to fluids, antihistamines, or corticosteroids.
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Topics

Pharmacologic Interventions

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