What is the recommended intramuscular (IM) treatment for an allergic reaction to an insect sting?

Intramuscular Treatment for Allergic Reaction to Insect Sting

Epinephrine (0.3-0.5 mg in adults, 0.01 mg/kg up to 0.3 mg in children) administered intramuscularly into the anterolateral aspect of the thigh is the first-line treatment for allergic reactions to insect stings, especially those involving systemic symptoms. 1, 2

Primary Treatment Algorithm

1. Immediate IM Epinephrine Administration

   • Adults and children ≥30 kg (66 lbs): 0.3-0.5 mg IM
   • Children <30 kg (66 lbs): 0.01 mg/kg IM (maximum 0.3 mg)
   • Inject into anterolateral thigh (through clothing if necessary) 2
   • May repeat every 5-10 minutes as necessary based on clinical response 2

2. Secondary Treatments (not substitutes for epinephrine)

   • H1 antihistamines
   • H2 antihistamines
   • Corticosteroids 1

Important Clinical Considerations

• Injection Technique: Use a needle long enough (at least 1/2 inch to 5/8 inch) to ensure intramuscular delivery 2
• Monitoring: Observe patients for at least 4-6 hours after treatment to monitor for delayed or biphasic reactions 1
• Repeat Dosing: Do not administer repeated injections at the same site due to risk of tissue necrosis from vasoconstriction 2
• No Contraindications: There is no contraindication to epinephrine use in a life-threatening situation such as anaphylaxis, even in patients with cardiovascular disease 3

Pitfalls and Caveats

• Common Error: Antihistamines and corticosteroids are often incorrectly used as first-line treatment. These are NOT substitutes for epinephrine in anaphylaxis 3
• Delayed Administration: Delayed use of epinephrine can lead to more serious anaphylaxis or treatment failure 3
• Route of Administration: IM injection in the anterolateral thigh achieves more rapid and higher plasma concentration than subcutaneous or IM injection in the arm 3
• Misuse of Aerosols: Epinephrine aerosols are not recommended for systemic reactions and can lead to serious complications if overused 4

Post-Emergency Care

• Patients with history of systemic reactions should:
  • Carry autoinjectable epinephrine
  • Be educated on proper use and indications
  • Be referred to an allergist-immunologist
  • Consider obtaining medical identification jewelry 3

Special Populations

• Children: Systemic reactions limited to skin manifestations in children under 16 years generally have good prognosis 1
• Cardiovascular Disease: Patients with cardiovascular disease experiencing anaphylaxis should still receive epinephrine 3
• Multiple Stings: May require more aggressive treatment and monitoring 1

The evidence strongly supports that intramuscular epinephrine is the cornerstone of treatment for allergic reactions to insect stings. While antihistamines and corticosteroids may help with symptom management, they should never delay or replace epinephrine administration in patients with systemic reactions.