What is the recommended treatment for a patient with anaphylaxis, particularly those with a history of allergies, asthma, or previous anaphylactic reactions?

Anaphylaxis Management

Intramuscular epinephrine is the only first-line treatment for anaphylaxis and must be administered immediately upon recognition—inject 0.3-0.5 mg (adults) or 0.01 mg/kg (children, maximum 0.3 mg prepubertal) into the mid-outer thigh (vastus lateralis) without delay. 1, 2, 3

Immediate Recognition and Action

When to suspect anaphylaxis:

• Sudden onset (minutes to hours) of multi-system symptoms after allergen exposure 2
• Key presentations include: respiratory symptoms (throat tightness, stridor, wheeze, difficulty breathing), cardiovascular symptoms (hypotension, tachycardia, syncope, collapse), skin symptoms (urticaria, angioedema, flushing), and gastrointestinal symptoms (vomiting, cramping, diarrhea) 2, 3
• Critical point: Even generalized urticaria alone after known allergen exposure (especially one that previously caused anaphylaxis) warrants epinephrine injection—do not wait for respiratory or cardiovascular symptoms to develop 1

High-risk patients requiring heightened vigilance:

• Adolescents and young adults (increased risk-taking behaviors, denial of symptoms) 1, 2
• Patients with asthma, especially severe or poorly controlled 1, 2
• Previous history of anaphylaxis 1
• Known allergies to peanuts, tree nuts, seafood, or milk 1
• Patients on beta-blockers 1

First-Line Treatment: Epinephrine Administration

Dosing and technique:

• Adults and adolescents >50 kg: 0.3-0.5 mg intramuscular (1:1000 concentration) 1, 2, 3
• Prepubertal children: 0.01 mg/kg intramuscular (maximum 0.3 mg) 1, 2
• Injection site: Mid-outer thigh (vastus lateralis muscle)—this produces higher and more rapid peak plasma levels than deltoid or subcutaneous routes 4, 2
• Repeat dosing: Every 5-15 minutes as needed if symptoms persist or recur; approximately 6-19% of pediatric patients require a second dose 1, 4, 2

Critical timing considerations:

• Inject epinephrine immediately when anaphylaxis is recognized—delayed administration is associated with increased mortality and biphasic reactions 1, 4, 2
• When uncertain about the diagnosis: Err on the side of injecting epinephrine rather than waiting; it is safer to give epinephrine unnecessarily than to withhold it when needed 1
• There are no absolute contraindications to epinephrine in anaphylaxis, even in patients with cardiac disease, advanced age, or pregnancy 4

Patient Positioning

• Place patient supine with lower extremities elevated to prevent cardiovascular collapse 4, 2
• If respiratory distress or vomiting present, position for comfort 2
• Never allow patient to stand, walk, or run—sudden postural changes can precipitate fatal cardiovascular collapse 2

Adjunctive Treatments (Only AFTER Epinephrine)

These are secondary interventions and should never delay or replace epinephrine:

• Oxygen: 6-8 L/min for respiratory symptoms 4, 2
• IV fluid resuscitation: Normal saline rapidly—5-10 mL/kg in first 5 minutes for adults (1-2 L total), up to 30 mL/kg in first hour for children 4, 2
• H1-antihistamines: Diphenhydramine (oral liquid formulations absorbed more rapidly than tablets) 2
• Albuterol: Nebulizer or MDI for persistent bronchospasm 2
• H2-antihistamines: May be added but are not essential 2

Important caveat: Antihistamines and bronchodilators do NOT treat the underlying pathophysiology of anaphylaxis and should never be used as initial or sole treatment 1, 2

Management of Refractory Anaphylaxis

For persistent hypotension despite epinephrine and fluids:

• Prepare epinephrine infusion: 4.0 μg/mL concentration, infuse at 1-4 μg/min, increase to maximum 10 μg/min if needed 1, 4
• Consider vasopressor infusion (dopamine) with continuous hemodynamic monitoring 2

For patients on beta-blockers unresponsive to epinephrine:

• Administer glucagon 1-5 mg IV over 5 minutes, followed by infusion of 5-15 μg/min 1, 4, 2
• Warning: Rapid glucagon administration can induce vomiting (not epinephrine) 2

For cardiopulmonary arrest:

• Initiate CPR and advanced cardiac life support with high-dose IV epinephrine and rapid volume expansion 4

Observation and Transfer

All patients must be transferred to emergency department for observation:

• Transport by EMS vehicle (not private car) 2
• Minimum observation period: 4-6 hours after symptom resolution 1, 4, 2
• Prolonged observation or admission warranted for:
  • Severe initial reaction requiring multiple epinephrine doses 1, 2
  • History of biphasic reactions 1, 2
  • Refractory symptoms 2
  • Patients on beta-blockers 1
  • Remote location with delayed access to care 1

Biphasic reactions:

• Can occur up to 72 hours after initial reaction (most within 6 hours) 1, 4
• Risk factors include severe initial reaction and need for >1 dose of epinephrine 1
• Early epinephrine administration may reduce biphasic reaction risk 4

Discharge Planning and Prevention

Before discharge, ensure:

• Two epinephrine autoinjectors prescribed with proper training on use (patients often fail to carry or use them) 1, 2
• Written anaphylaxis emergency action plan provided 1, 2
• Referral to allergist-immunologist for evaluation and prevention strategies 4, 2
• Medical identification jewelry or wallet card stating "anaphylaxis" and listing triggers 1

Autoinjector dosing for community use:

• Patients 7.5-25 kg: 0.15 mg autoinjector 1
• Patients 25-30 kg and above: 0.3 mg autoinjector 1
• Autoinjectors preferred over ampule/syringe in community settings due to ease of use and dosing accuracy 1

Common Pitfalls to Avoid

• Relying on antihistamines or albuterol as initial treatment—this is a common error that delays life-saving epinephrine 1
• Waiting for "classic" multi-system symptoms—inject epinephrine for isolated urticaria after known allergen exposure in high-risk patients 1
• Failing to prescribe epinephrine autoinjectors—patients with history of anaphylaxis, known sensitization to high-risk foods (peanut, tree nuts, seafood, milk), or insect venom allergy all require prescriptions 1
• Inadequate patient education—many patients fail to use autoinjectors due to fear of needles, concern about side effects, or failure to recognize symptoms 1
• Distinguishing from vasovagal reactions—vasovagal reactions present with bradycardia (not tachycardia) and lack cutaneous manifestations 4