What is the treatment for a patient with a systemic allergic reaction, possibly with a history of asthma or other respiratory conditions?

Treatment of Systemic Allergic Reaction (Anaphylaxis)

Administer epinephrine 0.3-0.5 mg intramuscularly (1:1000 dilution) into the anterolateral thigh immediately—this is the only first-line treatment and must not be delayed. 1, 2, 3

Immediate Management Algorithm

First-Line Treatment: Epinephrine

• Inject epinephrine IM into the mid-outer thigh at 0.3-0.5 mg for adults (0.01 mg/kg for children, maximum 0.3 mg) using 1:1000 concentration 2, 4, 3
• Repeat every 5-15 minutes as needed if symptoms persist or progress 1, 2, 5
• Do not delay epinephrine administration for any reason—delayed injection is associated with fatalities 1, 4
• Epinephrine is the only medication that acutely reverses anaphylaxis symptoms; antihistamines and corticosteroids are not substitutes 2, 4, 6

Immediate Supportive Measures

• Position patient supine with legs elevated (unless respiratory distress present, then position of comfort) 2, 4
• Establish IV access and administer crystalloid bolus: 500-1000 mL for adults or 20 mL/kg for children 2, 5
• Provide supplemental oxygen and monitor oxygen saturation continuously 2, 5
• Monitor vital signs closely: blood pressure, heart rate, respiratory rate, oxygen saturation 2, 5

Second-Line Adjunctive Medications

Antihistamines (After Epinephrine)

• H1-antagonist: Diphenhydramine 25-50 mg IV/IM (1-2 mg/kg) 1, 2, 5, 7
• H2-antagonist: Ranitidine 50 mg IV (or famotidine 20 mg IV if unavailable) 2, 5
• The combination of H1 + H2 antagonists is superior to H1 alone 2, 5
• These provide symptom relief but do not treat the acute life-threatening aspects of anaphylaxis 2, 7

Corticosteroids (After Epinephrine)

• Methylprednisolone 1-2 mg/kg IV every 6 hours (typically 40 mg IV every 6 hours for 70 kg adult) 1, 2, 5
• Alternative: Hydrocortisone 100 mg IV 2
• Corticosteroids provide no acute benefit but may prevent biphasic reactions (occurring in up to 20% of cases) 2, 5, 4
• Never use corticosteroids as first-line treatment instead of epinephrine 5

Management of Persistent Symptoms

For Refractory Hypotension

• If hypotension persists despite epinephrine and adequate fluid resuscitation, consider epinephrine IV infusion at 5-15 μg/min 2
• Alternative vasopressors: Dopamine 2-20 μg/kg/min or vasopressin 0.01-0.04 U/min 2, 5

For Persistent Bronchospasm

• Administer albuterol nebulization 2.5-5 mg in 3 mL saline if bronchospasm is unresponsive to epinephrine 2

Special Population: Patients on Beta-Blockers

• These patients are at higher risk for severe anaphylaxis and may be refractory to epinephrine 1
• If unresponsive to multiple epinephrine doses and fluids, administer glucagon 1-5 mg IV over 5 minutes (20-30 μg/kg for children, maximum 1 mg), followed by infusion at 5-15 μg/min 1, 2, 5
• Glucagon bypasses beta-receptors and can reverse refractory bronchospasm and hypotension 1, 2

High-Risk Patients Requiring Extra Caution

Asthma Patients

• Patients with asthma, particularly poorly controlled asthma, are at higher risk for serious systemic reactions 1
• Consider measuring peak expiratory flow rate before any allergen exposure; withhold allergen immunotherapy if significantly below baseline 1
• These patients may require longer observation periods and should carry injectable epinephrine 1

Observation and Monitoring

Duration of Observation

• Observe all patients for minimum 4-6 hours after symptom resolution 2, 4
• Extend observation to at least 24 hours for severe reactions 5
• Biphasic reactions can occur up to 72 hours after initial reaction (average 11 hours), with higher risk in patients requiring multiple epinephrine doses 5, 4
• Most initial reactions occur within 20-30 minutes, but late reactions do occur 1

Discharge Planning

Mandatory Prescriptions

• Two epinephrine auto-injectors (0.15 mg if 10-25 kg, 0.3 mg if ≥25 kg) with hands-on training demonstration 2, 4
• Prednisone 1 mg/kg daily (maximum 60-80 mg) for 2-3 days (no taper needed for short course) 2
• H1-antihistamine for 2-3 days 2
• H2-antihistamine (ranitidine) twice daily for 2-3 days 2

Patient Education and Follow-Up

• Provide written anaphylaxis emergency action plan 2, 4
• Educate on recognition of early symptoms and proper auto-injector technique 2, 4
• Consider medical identification jewelry 4
• Schedule follow-up with allergist within 1-2 weeks for formal allergy testing and long-term management 2, 4

Critical Pitfalls to Avoid

• Never delay or withhold epinephrine while waiting for IV access or other interventions 1, 5, 4
• Never substitute antihistamines or bronchodilators for epinephrine as first-line treatment 2, 5, 4
• Never administer epinephrine IV in non-cardiac arrest situations without adequate monitoring 5
• Never discharge patients prematurely without adequate observation for biphasic reactions 5, 4
• Never prescribe corticosteroids alone without epinephrine auto-injectors 2
• Do not use subcutaneous epinephrine—intramuscular administration in the thigh provides faster, more reliable absorption 2, 3

Setting Requirements

• Anaphylaxis treatment must occur in a facility with trained personnel, immediate physician availability, and equipment for managing anaphylaxis 1
• Required equipment includes: stethoscope, sphygmomanometer, tourniquets, syringes, large-bore IV catheters (14-18 gauge), aqueous epinephrine 1:1000, oxygen delivery equipment, IV fluid setup, injectable antihistamines, injectable corticosteroids, airway management equipment, and glucagon kit 1
• Regular practice drills for handling systemic reactions should be conducted 1