What are the recommended dosages for steroids and antihistamines in the management of acute allergic reactions?

Recommended Dosages for Steroids and Antihistamines in Acute Allergic Reactions

For acute allergic reactions, epinephrine is the first-line treatment (1 mg/mL solution), with diphenhydramine 25-50 mg as adjunctive therapy, and prednisone 0.5-1 mg/kg for preventing biphasic reactions. 1

First-Line Treatment: Epinephrine

Adults and Children ≥30 kg (66 lbs):

• 0.3-0.5 mg (0.3-0.5 mL of 1:1000 solution) intramuscularly into anterolateral thigh 2
• May repeat every 5-10 minutes as necessary 1

Children <30 kg (66 lbs):

• 0.01 mg/kg (0.01 mL/kg of 1:1000 solution), maximum 0.3 mg 2
• May repeat every 5-10 minutes as necessary 1

Second-Line Treatment: Antihistamines

H1 Antihistamines:

• Adults and children >12 years: Diphenhydramine 25-50 mg (1-2 mg/kg) orally or parenterally 1, 3
• Children 6-12 years: Diphenhydramine 25 mg (1-2 mg/kg) orally or parenterally 1, 3
• Children <6 years: Diphenhydramine 1-2 mg/kg (not to exceed 50 mg) parenterally 1, 3
• Dosing frequency: Every 4-6 hours 3
• Alternative: Less-sedating second-generation antihistamine (e.g., cetirizine 10 mg) 1

H2 Antihistamines:

• Adults: Ranitidine 50 mg IV or oral 1
• Children: Ranitidine 1 mg/kg (12.5-50 mg) IV or oral 1
• Note: In anaphylaxis management, combination of H1 and H2 antihistamines is superior to H1 alone 1

Corticosteroids:

For preventing biphasic or protracted reactions:

• Intravenous administration:

  • Methylprednisolone 1.0-2.0 mg/kg/day divided every 6 hours 1

• Oral administration:

  • Prednisone 0.5 mg/kg daily for 2-3 days 1
  • For less critical episodes: Prednisone 20 mg orally every 12 hours for 4 days 4

Important Clinical Considerations:

• Epinephrine is the ONLY first-line treatment for anaphylaxis; antihistamines and corticosteroids should never be used alone 1
• Early administration of epinephrine is associated with fewer uncontrolled reactions and hospital admissions 5
• Antihistamines only relieve itching and urticaria but do not treat respiratory distress or hypotension 1
• Corticosteroids have a delayed onset of action (4-6 hours) and are not helpful in acute management but may prevent biphasic reactions 1
• Treatment with corticosteroids should be limited to 2-3 days as all reported biphasic reactions occur within this timeframe 1

Special Situations:

For patients on β-blockers with refractory symptoms:

• Glucagon 1-5 mg IV (adults) or 20-30 μg/kg up to 1 mg (children) over 5 minutes 1
• May follow with infusion of 5-15 μg/min titrated to clinical response 1

For refractory bronchospasm:

• Albuterol 2.5-5 mg in 3 mL saline via nebulizer, repeat as necessary 1

For refractory hypotension:

• IV fluids for volume replacement 1
• Consider vasopressors (e.g., dopamine 2-20 μg/kg/min) if unresponsive to epinephrine and fluids 1

Common Pitfalls to Avoid:

• Delaying epinephrine administration in favor of antihistamines 5
• Injecting epinephrine into buttocks, digits, hands, or feet 2
• Using oral antihistamines in patients with severe dysphagia or respiratory distress 6
• Relying on corticosteroids for immediate symptom relief 1
• Discontinuing observation too early (monitor for 4-6 hours minimum after reaction) 1