A 28-year-old woman presents to the emergency department with acute onset of angioedema of the lips and tongue, urticaria, and stridor 15 minutes after receiving intravenous penicillin for a urinary tract infection. She has no prior history of drug allergy. Vital signs: BP 95/60 mmHg, HR 120/min, RR 28/min. What is the most appropriate immediate next step in management?

Explanation

## Clinical Presentation & Diagnosis This is a **Type I hypersensitivity reaction (anaphylaxis)** triggered by penicillin. The key clinical features are: - Acute onset (within 15 minutes of drug exposure) - Angioedema of airway structures (lips, tongue, stridor) - Urticaria (mast cell and basophil degranulation) - **Hemodynamic instability** (hypotension, tachycardia) **Key Point:** Anaphylaxis is a medical emergency. The presence of **airway involvement + hypotension** defines this as severe anaphylaxis requiring immediate epinephrine. ## Why Epinephrine Is First-Line **High-Yield:** Epinephrine is the **only drug that addresses all pathophysiologic features** of anaphylaxis: - **α-adrenergic effects:** vasoconstriction → reverses hypotension, reduces angioedema - **β-adrenergic effects:** bronchodilation, stabilizes mast cells (prevents further mediator release) - **Timing:** must be given **within minutes** of symptom onset to prevent progression to cardiovascular collapse or complete airway obstruction **Clinical Pearl:** The IM route (anterolateral thigh) is preferred over IV because it provides more sustained absorption and is safer in a moving/agitated patient. IV epinephrine is reserved for profound shock or cardiac arrest. ## Management Algorithm ```mermaid flowchart TD A[Acute anaphylaxis: airway + hemodynamic signs]:::outcome --> B{Epinephrine given?}:::decision B -->|No| C[IM epinephrine 0.3-0.5 mg 1:1000 immediately]:::action B -->|Yes| D[Reassess airway, breathing, circulation]:::action C --> E[Establish IV access, place supine with legs elevated]:::action E --> F[Antihistamines + corticosteroids as adjuncts]:::action D --> G{Improving?}:::decision G -->|No| H[Repeat epinephrine every 5-15 min as needed]:::action G -->|Yes| I[Observe 4-8 hours for biphasic reaction]:::action ``` **Key Point:** Antihistamines and corticosteroids are **adjunctive only** — they do not reverse the acute hemodynamic or airway effects and should never delay epinephrine. ## Dose & Route | Parameter | Value | | --- | --- | | **Dose (IM)** | 0.3–0.5 mg of 1:1000 solution | | **Route** | Intramuscular (anterolateral thigh preferred) | | **Repeat interval** | Every 5–15 minutes if symptoms persist | | **IV route** | Reserved for shock/cardiac arrest (0.1 mg of 1:10,000 solution) | [cite:Robbins 10e Ch 6]