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Difficulty: MediumGeneral Internal Medicine

A 4545-year-old man is hospitalized for community-acquired pneumonia. Ten minutes after starting his first dose of intravenous ceftriaxone, he develops sudden-onset diffuse urticaria, shortness of breath, and throat tightness. His temperature is 37.2∘C37.2^{\circ}\text{C} (99.0∘F99.0^{\circ}\text{F}), blood pressure is 82/50 mm Hg82/50\text{ mm Hg}, pulse is 124/min124/\text{min}, and respiratory rate is 26/min26/\text{min}. Oxygen saturation is 90%90\% on room air. Examination reveals diffuse expiratory wheezing and facial angioedema. Arrange the following steps in the most appropriate chronological order for the acute management of this patient's condition.

  1. 1Immediately discontinue the intravenous ceftriaxone infusion
  2. 2Administer intramuscular epinephrine to the mid-anterolateral thigh
  3. 3Administer a rapid intravenous bolus of isotonic crystalloid
  4. 4Administer intravenous methylprednisolone and diphenhydramine

Answer

The correct sequence is to first discontinue the offending medication, followed immediately by intramuscular epinephrine, then intravenous fluid resuscitation, and finally adjunctive therapies like corticosteroids and antihistamines.
In the setting of anaphylaxis triggered by an intravenous infusion, the most appropriate chronological sequence ensures life-saving interventions are prioritized. Discontinuing the offending agent (ceftriaxone) prevents further allergen exposure and mast cell degranulation. Immediately following this, intramuscular epinephrine is the primary drug of choice to reverse the life-threatening features of anaphylaxis (bronchospasm, upper airway edema, and hypotension) via its potent alpha-1 and beta-2 adrenergic effects. Once epinephrine is administered, attention must turn to restoring circulating volume with rapid intravenous isotonic crystalloids, as anaphylaxis causes profound distributive shock due to increased capillary permeability. Finally, adjunctive therapies such as intravenous corticosteroids (methylprednisolone) and antihistamines (diphenhydramine) are administered. These agents have a delayed onset of action and do not acutely reverse shock or airway obstruction, but they are critical for controlling cutaneous symptoms and preventing biphasic reactions.

Step-by-Step Solution

1
Halt the intravenous ceftriaxone infusion.
Allergen exposure is immediately stopped.
Prevents further IgE-mediated degranulation of mast cells and basophils.
2
Inject intramuscular epinephrine.
Alpha-1, beta-1, and beta-2 adrenergic receptors are stimulated.
Rapidly reverses systemic vasodilation, increases cardiac inotropy, and relieves life-threatening bronchospasm and mucosal edema.
3
Infuse a rapid intravenous bolus of normal saline or lactated Ringer's.
Intravascular volume is expanded.
Treats the profound distributive shock caused by massive capillary leak and vasodilation, restoring blood pressure.
4
Give intravenous glucocorticoids (methylprednisolone) and H1/H2 blockers (diphenhydramine, famotidine).
Histamine receptors are blocked and inflammatory cascades are suppressed.
Provides symptomatic relief for urticaria and mitigates potential late-phase (biphasic) allergic responses.

Key Concept

The acute management of inpatient anaphylaxis prioritizes immediate removal of the trigger and administration of intramuscular epinephrine before proceeding to fluid resuscitation and delayed-onset adjunctive medications.
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General Internal Medicine

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