What is the immediate treatment for a hypersensitivity reaction with symptoms of anaphylaxis?

Immediate Treatment for Anaphylaxis

The immediate treatment for hypersensitivity reactions with symptoms of anaphylaxis is prompt administration of intramuscular epinephrine into the lateral thigh, which should be given without delay as the first-line life-saving intervention. 1, 2

Recognition of Anaphylaxis

Anaphylaxis presents with the following symptoms:

• Respiratory: Dyspnea, stridor, wheezing, cough, dysphonia
• Cardiovascular: Hypotension, syncope, tachycardia
• Cutaneous: Diffuse erythema, pruritus, urticaria, angioedema
• Gastrointestinal: Nausea, vomiting, diarrhea
• Other: Lightheadedness, headache, feeling of impending doom, unconsciousness 1

Treatment Algorithm

First-Line Treatment:

1. Administer epinephrine immediately

   • Dose: 0.01 mg/kg of 1:1000 concentration (1 mg/mL)
   • Maximum single dose: 0.5 mg for adults >50 kg
   • Route: Intramuscular injection into the vastus lateralis (anterolateral thigh)
   • May repeat every 5 minutes as necessary 1, 2

2. Autoinjector options:

   • 0.3 mg for adults and children >25-30 kg
   • 0.15 mg for children weighing 10-25 kg 2

3. Simultaneously:

   • Stop exposure to trigger (if ongoing)
   • Activate emergency response system
   • Position patient appropriately (supine or Trendelenburg if hypotensive)
   • Maintain airway, breathing, circulation 1

Second-Line Treatments (after epinephrine):

1. Oxygen: Administer supplemental oxygen (8-10 L/min via face mask) for respiratory symptoms 2

2. Fluid resuscitation: For hypotension, give rapid IV fluids (20 mL/kg normal saline bolus), which may need to be repeated 2

3. Antihistamines: H1 antihistamines (e.g., diphenhydramine) for cutaneous symptoms only 1, 2

4. Additional epinephrine: If symptoms persist and EMS arrival will exceed 5-10 minutes, consider a repeat dose 1

Important Clinical Considerations

• No absolute contraindications exist for using epinephrine to treat anaphylaxis, even in patients with cardiac disease, advanced age, or frailty 1

• Intramuscular route is preferred over subcutaneous for faster absorption, though both are acceptable in emergency situations 1

• Delay in administering epinephrine has been associated with anaphylaxis fatalities and increased risk of biphasic reactions 1

• Antihistamines and corticosteroids are not first-line treatments and should never delay epinephrine administration 1, 2

• Glucocorticoids have no role in treating acute anaphylaxis due to their slow onset of action (4-6 hours) 1, 2

Common Pitfalls to Avoid

1. Misdiagnosis: Vasovagal reactions can be confused with anaphylaxis but typically present with bradycardia (not tachycardia), absence of urticaria, and cool/pale skin 1

2. Delayed epinephrine administration: Hesitation in giving epinephrine due to unfounded concerns about adverse effects can lead to poor outcomes 1

3. Relying on antihistamines alone: H1 antihistamines address only cutaneous manifestations, which are not life-threatening 1

4. Premature discharge: Patients should be observed until symptoms fully resolve and should be educated about the possibility of biphasic reactions, which can occur up to 72 hours later 1

5. Failure to prescribe autoinjectors: Patients with anaphylaxis should be prescribed epinephrine autoinjectors upon discharge 2

Remember that anaphylaxis occurs on a continuum, and symptoms that are not immediately life-threatening may progress rapidly unless treated promptly with epinephrine 1.