A 28-year-old woman presents to the emergency department with acute onset of urticaria, angioedema of lips and tongue, and stridor 15 minutes after receiving intravenous penicillin for a urinary tract infection. She denies prior drug allergies. Vital signs: BP 92/58 mmHg, HR 118/min, RR 24/min. What is the most appropriate immediate next step in management?

Question

Accepted Answer

B. Administer 0.3–0.5 mg of 1:1000 epinephrine intramuscularly immediately. ## Clinical Recognition

This is a classic presentation of **Type I hypersensitivity (anaphylaxis)** triggered by penicillin:
- Rapid onset (15 minutes post-exposure)
- Urticaria + angioedema + airway involvement (stridor)
- Hemodynamic compromise (hypotension, tachycardia)

## Immediate Management Algorithm

```mermaid
flowchart TD
  A[Anaphylaxis suspected]:::outcome --> B{Airway/Breathing/Circulation compromised?}:::decision
  B -->|Yes| C[IM Epinephrine 0.3-0.5 mg 1:1000]:::action
  B -->|No| D[Still give IM Epinephrine if any systemic signs]:::action
  C --> E[Lay supine, elevate legs]:::action
  E --> F[IV access, fluid resuscitation]:::action
  F --> G[H1 blocker + corticosteroid]:::action
  G --> H[Observe 4-8 hours minimum]:::action
```

**Key Point:** Epinephrine is the first-line, life-saving drug in anaphylaxis. Delay increases mortality risk.

**High-Yield:** The correct dose is **0.3–0.5 mg of 1:1000 epinephrine IM** (not IV, not subcutaneous). Repeat every 5–15 minutes if needed.

**Clinical Pearl:** Antihistamines and corticosteroids are **adjunctive**, not primary. They do not replace epinephrine and should not delay its administration.

**Warning:** Skin prick testing during acute anaphylaxis is contraindicated and dangerous. Testing is done only after full recovery, weeks later, if allergy confirmation is needed.

## Why Epinephrine Works

| Mechanism | Effect |
|-----------|--------|
| α1-adrenergic | Vasoconstriction → ↑ BP, ↓ angioedema |
| β2-adrenergic | Bronchodilation, ↓ mast cell degranulation |
| β1-adrenergic | ↑ cardiac output, HR |

**Mnemonic: ABCDE of Anaphylaxis Management** — **A**irway, **B**reathing, **C**irculation (Epinephrine first), **D**rugs (H1/H2/steroids second), **E**levate legs, **E**voke history.

[cite:Harrison 21e Ch 317]

Answer

A. Perform skin prick testing to confirm penicillin allergy

Answer

C. Start intravenous antihistamines and observe for 2 hours

Answer

D. Administer intravenous hydrocortisone 100 mg and monitor

Explanation

Clinical Recognition

Immediate Management Algorithm

Why Epinephrine Works

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Mechanism	Effect
α1-adrenergic	Vasoconstriction → ↑ BP, ↓ angioedema
β2-adrenergic	Bronchodilation, ↓ mast cell degranulation
β1-adrenergic	↑ cardiac output, HR