A 28-year-old woman presents to the emergency department 15 minutes after eating peanuts at a restaurant. She complains of severe itching of the lips and throat, followed by facial angioedema and wheezing. Her blood pressure is 90/60 mmHg, heart rate 118/min, and respiratory rate 24/min. She has a history of similar reactions to tree nuts. What is the most appropriate immediate next step in management?

Explanation

## Immediate Management of Anaphylaxis **Key Point:** Anaphylaxis is a life-threatening Type I hypersensitivity reaction requiring immediate intramuscular epinephrine as first-line therapy, regardless of severity. ### Clinical Presentation Recognition This patient exhibits classic anaphylaxis features: - Rapid onset (within 15 minutes of allergen exposure) - Cutaneous symptoms (angioedema, pruritus) - Respiratory involvement (wheezing, stridor risk) - Cardiovascular compromise (hypotension, tachycardia) ### Why Epinephrine is Mandatory Epinephrine is the **only drug that addresses the underlying pathophysiology** of anaphylaxis: | Mechanism | Effect | |-----------|--------| | α-adrenergic action | Reverses vasodilation, restores BP | | β~1~-adrenergic action | Increases cardiac output, improves perfusion | | β~2~-adrenergic action | Relaxes bronchial smooth muscle, reduces wheeze | | Mast cell stabilization | Prevents further mediator release | **High-Yield:** Epinephrine must be given **intramuscularly (IM)** into the anterolateral thigh (0.3–0.5 mg of 1:1000 solution) — NOT subcutaneously or intravenously in the acute phase. IM route ensures rapid absorption and peak effect within 5–15 minutes. ### Timeline of Anaphylaxis Management ```mermaid flowchart TD A[Anaphylaxis suspected]:::urgent --> B[IM epinephrine 0.3-0.5 mg<br/>1:1000 immediately]:::action B --> C[Lay patient flat,<br/>elevate legs]:::action C --> D[Establish IV access,<br/>give normal saline bolus]:::action D --> E{Response adequate?}:::decision E -->|Yes| F[Observe 4-8 hours<br/>for biphasic reaction]:::outcome E -->|No| G[Repeat epinephrine<br/>every 5-15 min]:::action F --> H[Discharge with<br/>EpiPen + antihistamine]:::action ``` **Clinical Pearl:** Antihistamines and corticosteroids are **adjunctive only** — they do NOT treat acute anaphylaxis and should never delay epinephrine. They are given AFTER epinephrine to prevent biphasic reactions and manage residual symptoms. **Warning:** Delaying epinephrine to give antihistamines or corticosteroids first is a common fatal error in anaphylaxis management. ### Subsequent Supportive Care (After Epinephrine) 1. IV access and normal saline 0.5–1 L bolus 2. Antihistamine: diphenhydramine 50 mg IV or chlorpheniramine 10 mg IV 3. Corticosteroid: methylprednisolone 125 mg IV or hydrocortisone 200 mg IV 4. Observation for ≥4–8 hours (risk of biphasic anaphylaxis in 1–3% of cases) [cite:Harrison 21e Ch 317]