What is the treatment for a biphasic anaphylactic reaction?

Treatment of Biphasic Anaphylactic Reaction

Epinephrine is the first-line pharmacotherapy for biphasic anaphylaxis, administered immediately upon recognition of symptoms without delay, just as with the initial anaphylactic reaction. 1

Understanding Biphasic Anaphylaxis

Biphasic anaphylaxis occurs when the initial symptoms of anaphylaxis resolve completely but then recur up to 72 hours later, with a mean recurrence time of 11 hours 1. Approximately 10.3% of patients with anaphylaxis may develop biphasic reactions 1.

Treatment Algorithm

Immediate Management

1. Administer epinephrine intramuscularly:

   • Adults and children ≥30 kg: 0.3-0.5 mg of 1:1000 concentration (1 mg/mL) 2
   • Children <30 kg: 0.01 mg/kg of 1:1000 concentration (1 mg/mL), maximum 0.3 mg 2
   • Inject into the vastus lateralis in the anterolateral thigh for optimal absorption 1
   • Repeat every 5-15 minutes if symptoms persist 1

2. Position the patient appropriately:

   • Supine with legs elevated if hypotensive 2
   • Trendelenburg position for severe hypotension 1

3. Administer fluid resuscitation:

   • Begin immediately in patients with hypotension 1
   • 1-2 liters of normal saline at 5-10 mL/kg in the first 5 minutes 2

4. Provide supplemental oxygen:

   • For patients with respiratory symptoms 1
   • For patients receiving multiple doses of epinephrine 1

Adjunctive Therapy

• Antihistamines (H1 and H2 blockers):

  • May be administered for cutaneous manifestations 1
  • Should never delay or replace epinephrine 1
  • Not reliable for preventing biphasic anaphylaxis 1

• Glucocorticoids:

  • Not recommended for preventing biphasic anaphylaxis 1
  • Have no role in treating acute anaphylaxis due to slow onset of action 1

• For persistent bronchospasm:

  • Administer inhaled beta-2 agonists (albuterol 2.5-5 mg via nebulizer) 1, 2

Severe or Refractory Cases

• For protracted anaphylaxis:
  • Consider intravenous epinephrine infusion (1:10,000 concentration [1 mg/10 mL]) 1
  • Initial rate of 5-15 μg/min, carefully titrated 2

Monitoring and Observation

Risk Assessment for Biphasic Reactions

High-risk factors include:

• Severe initial anaphylactic reaction 1
• Requirement of more than one dose of epinephrine (OR = 4.82) 1
• Wide pulse pressure 1
• Unknown anaphylaxis trigger 1
• Cutaneous signs and symptoms 1
• Drug trigger in children 1
• History of prior anaphylaxis 3
• Symptoms of diarrhea or wheezing 3

Observation Period

• All patients: Observe until signs and symptoms have fully resolved 1
• High-risk patients: Extended observation of up to 6 hours or longer (including hospital admission) 1
• Low-risk patients: Discharge after a 1-hour asymptomatic observation may be reasonable 1

Patient Education and Discharge Planning

1. Prescribe epinephrine auto-injector with proper training on use 2
2. Provide education on:
   • Risk of biphasic reactions occurring up to 72 hours after initial reaction 1
   • Signs and symptoms of anaphylaxis 1
   • Proper use of epinephrine auto-injector 2
   • Importance of seeking immediate medical attention if symptoms recur 1
3. Refer to an allergist/immunologist for identification of triggers and long-term management 2

Important Caveats

• Delay in administering epinephrine has been associated with anaphylaxis fatalities and increased risk of biphasic reactions 1
• There are no absolute contraindications to epinephrine use for anaphylaxis, even in elderly patients or those with cardiac disease 2
• The estimated number needed to monitor with extended observation to detect one episode of biphasic anaphylaxis is 13 for patients requiring multiple epinephrine doses 1
• Biphasic reactions can be life-threatening, with up to 50% requiring treatment with epinephrine 4

Remember that prompt recognition and immediate epinephrine administration are the cornerstones of effective management for both initial and biphasic anaphylactic reactions.