What is the ER treatment of choice for a 45-year-old female patient presenting with bilateral hand wasp stings and a wasp sting to the chest, with swelling and erythema on the hands and mild erythema on the chest, who has been taking Benadryl (diphenhydramine) with some relief?

Emergency Treatment for Wasp Stings

Intramuscular epinephrine is the first-line treatment for this patient with multiple wasp stings presenting with significant local reactions and potential for systemic symptoms. 1, 2

Initial Assessment and Management

1. Assess for signs of anaphylaxis:

   • Respiratory compromise (dyspnea, wheezing, stridor)
   • Hypotension or associated symptoms (syncope, dizziness)
   • Widespread urticaria beyond sting sites
   • Gastrointestinal symptoms (vomiting, abdominal pain)

2. Treatment algorithm:

   • For signs of anaphylaxis or significant systemic reaction:

     • Administer epinephrine 0.3-0.5 mg IM in the anterolateral thigh immediately 1, 3
     • Place patient on cardiac monitor and establish IV access
     • Consider supplemental oxygen if respiratory symptoms present

   • For localized reactions (as in this case with bilateral hand swelling/erythema):

     • H1 antihistamines: Continue diphenhydramine 25-50 mg every 6 hours 3
     • Add H2 antihistamine: Ranitidine 150 mg twice daily 3, 4
     • Consider corticosteroids: Prednisone 40-60 mg daily for 2-3 days 3, 1
     • Local wound care: Clean with soap and water 1
     • Cold compresses to reduce swelling and pain 1

Medication Details

• Epinephrine: Intramuscular injection provides faster absorption than subcutaneous administration. Peak plasma concentration occurs in approximately 8 minutes when administered in the lateral thigh versus 34 minutes for subcutaneous administration 3

• Antihistamines: While diphenhydramine has been providing some relief, consider:

  • Continuing diphenhydramine for immediate symptom control
  • Adding an H2 blocker (ranitidine) for enhanced effect 3, 4
  • Consider transitioning to non-sedating antihistamines (cetirizine, fexofenadine) for ongoing management if needed 5

Monitoring and Disposition

• Observe for at least 4-6 hours after treatment, especially if epinephrine is administered 3
• Monitor for signs of infection at sting sites
• Elevation of affected extremities to reduce swelling

Discharge Planning

If symptoms improve and no signs of anaphylaxis develop:

• Prescribe epinephrine auto-injector (2 doses) if any systemic symptoms develop during observation 3, 1
• Continue H1 antihistamine (diphenhydramine every 6 hours or non-sedating alternative) for 2-3 days 3
• Continue H2 antihistamine (ranitidine twice daily) for 2-3 days 3
• Prednisone daily for 2-3 days 3
• Provide education on:
  • Signs of delayed or biphasic reactions
  • When to return to emergency care
  • Proper wound care and monitoring for infection

Important Considerations

• Pitfall to avoid: Relying solely on antihistamines for treatment of potential anaphylaxis. Epinephrine is the first-line treatment for anaphylaxis, as antihistamines have a slow onset of action (1+ hour) and primarily relieve cutaneous symptoms 3

• Caution: Even though this patient currently has localized reactions, multiple stings (especially to different body areas) increase the risk of systemic reactions 1

• Follow-up: Recommend follow-up with primary care physician within 2-3 days, and consider referral to an allergist-immunologist if systemic symptoms develop 1