## Anaphylaxis Management — First-Line Drug **Key Point:** Epinephrine (adrenaline) is the only first-line, life-saving drug for anaphylaxis. It must be given IM (not IV) at a dose of 0.3–0.5 mg in adults, repeated every 5–15 minutes if needed. ### Mechanism of Action Epinephrine acts as: - **α₁-agonist:** Causes vasoconstriction, reducing angioedema and restoring blood pressure - **β₂-agonist:** Bronchodilation, reversing bronchospasm - **β₁-agonist:** Increases cardiac output and heart rate - **Stabilises mast cells:** Reduces further degranulation and mediator release ### Why IM Route? - IM absorption is rapid and reliable in anaphylaxis - IV administration risks severe hypertension and arrhythmias - IM allows for repeat dosing if symptoms persist ### Timing and Sequence 1. **Immediate:** Epinephrine IM (0.3–0.5 mg) 2. **Concurrent:** Lay patient flat, elevate legs, establish IV access, give oxygen 3. **5–15 min later:** Repeat epinephrine if symptoms persist 4. **After stabilisation:** Add antihistamines (H₁ + H₂ blockers) and corticosteroids to prevent biphasic reactions **High-Yield:** Antihistamines and corticosteroids are **adjunctive**, not first-line. They do NOT replace epinephrine and should never delay its use. **Clinical Pearl:** Delayed or absent epinephrine use is the most common cause of fatal anaphylaxis. Even mild urticaria + respiratory symptoms = anaphylaxis until proven otherwise. **Warning:** Do NOT give IV epinephrine in anaphylaxis outside ICU/resuscitation settings — risk of coronary vasospasm, MI, and malignant arrhythmias. [cite:Harrison 21e Ch 297]
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