What medications can be given to a patient with an allergic reaction after administering epinephrine (adrenaline) to help alleviate symptoms?

Management of Allergic Reactions After Epinephrine Administration

After administering epinephrine for an allergic reaction, additional medications including H1 antihistamines, H2 antihistamines, corticosteroids, and bronchodilators should be given to help alleviate symptoms and prevent biphasic reactions.

First-Line Treatment Reminder

• Epinephrine is the first-line treatment for anaphylaxis and should never be delayed 1
• Administered intramuscularly in the anterolateral thigh at 0.01 mg/kg (1:1000 solution), up to 0.3 mg in children and 0.3-0.5 mg in adults 2
• Can be repeated every 5-15 minutes if symptoms persist 2, 1

Secondary Medications (After Epinephrine)

H1 Antihistamines

• Diphenhydramine 1-2 mg/kg or 25-50 mg IV/IM in adults 2, 1
• Effective for cutaneous symptoms (urticaria, angioedema, pruritus)
• Note: H1 antihistamines are second-line therapy and should never be administered alone in anaphylaxis 2

H2 Antihistamines

• Ranitidine 50 mg IV in adults and 12.5-50 mg (1 mg/kg) in children 2
• Can be diluted in 5% dextrose to 20 mL and injected over 5 minutes
• Combination of H1 and H2 antagonists is superior to H1 antagonists alone 2

Corticosteroids

• Consider systemic glucocorticosteroids for patients with:
  • History of idiopathic anaphylaxis
  • Asthma
  • Severe or prolonged anaphylaxis 2
• IV glucocorticosteroids: 1-2 mg/kg/day equivalent, administered every 6 hours 2
• Oral prednisone (0.5 mg/kg) may be sufficient for less critical episodes 2
• Note: Corticosteroids have slow onset and are not helpful acutely but may prevent recurrent/biphasic reactions 2

Bronchodilators

• For persistent bronchospasm resistant to epinephrine:
• Nebulized albuterol 2.5-5 mg in 3 mL saline, repeated as necessary 2

Management of Specific Complications

Refractory Hypotension

• Continue fluid resuscitation with normal saline (1-2 L at 5-10 mL/kg in first 5 minutes) 2
• For hypotension unresponsive to epinephrine and fluids, consider vasopressor infusion:
  • Dopamine (400 mg in 500 mL of 5% dextrose) at 2-20 μg/kg/min 2
  • Titrate to maintain systolic BP >90 mmHg 2

For Patients on Beta-Blockers

• Consider glucagon if standard treatment is ineffective
• Dosage: 1-5 mg IV over 5 minutes, followed by infusion (5-15 μg/min) 2

Monitoring and Observation

• Monitor vital signs until complete resolution of symptoms 2
• Observe for at least 4-6 hours after symptom resolution due to risk of biphasic reactions 1
• Severe reactions may require 24-hour observation 2

Special Considerations

• Recent research supports the beneficial effect of both epinephrine and antihistamines in managing allergic reactions 3
• The combination of diphenhydramine and ranitidine is superior to diphenhydramine alone but should never replace epinephrine 2
• Patients with history of severe reactions should be prescribed epinephrine auto-injectors upon discharge 1, 4

Common Pitfalls to Avoid

• Delaying epinephrine administration (associated with fatal outcomes) 2
• Using antihistamines or corticosteroids as substitutes for epinephrine 2, 1
• Failing to monitor patients adequately for biphasic reactions 2
• Not addressing respiratory symptoms with bronchodilators when needed 2
• Underestimating the psychological impact of allergic reactions (43% of patients report fear for their lives) 5

By following this algorithmic approach to managing allergic reactions after epinephrine administration, clinicians can effectively reduce morbidity and mortality while improving patient outcomes.