What is the treatment for insect bite allergy?

Treatment for Insect Bite Allergy

For systemic reactions including anaphylaxis, immediately administer intramuscular epinephrine 0.3-0.5 mg in adults (0.01 mg/kg up to 0.3 mg in children) into the anterolateral thigh and activate emergency medical services, as delayed epinephrine administration is associated with fatal outcomes. 1, 2, 3

Acute Management by Reaction Severity

Systemic/Anaphylactic Reactions

Epinephrine is the only first-line treatment for anaphylaxis and must be given immediately for any systemic symptoms including difficulty breathing, tongue/throat swelling, hypotension, widespread urticaria, or cardiovascular symptoms. 1, 2, 3

• Administer intramuscular epinephrine in the anterolateral thigh (not subcutaneous or arm injection), as this route achieves faster and higher plasma concentrations. 2
• Dosing: 0.3-0.5 mg in adults; 0.01 mg/kg (maximum 0.3 mg) in children. 2, 4
• Be prepared to repeat the dose in 10-20 minutes if symptoms persist or worsen. 2
• Place patient in recumbent position with legs elevated if hypotension develops. 2
• Transport to emergency department immediately for supportive therapy and observation for biphasic reactions. 1, 2

Adjunctive treatments (these do NOT replace epinephrine):

• Oral antihistamines may reduce itching but have minimal immediate effect on life-threatening symptoms. 2
• Consider oral corticosteroids to prevent biphasic reactions, though they have no immediate effect. 2

Large Local Reactions

Large local reactions present with swelling >10 cm in diameter contiguous to the sting site, increasing in size over 24-48 hours and persisting 5-10 days. 1

• Initiate a short course of oral corticosteroids promptly (within the first 24-48 hours) to limit progression of swelling, though controlled trial evidence is lacking. 1, 4
• Apply cold compresses or ice packs to reduce pain and swelling. 1, 2, 5
• Give oral antihistamines to reduce itching and discomfort. 1, 2, 5
• Provide oral analgesics (acetaminophen or ibuprofen) for pain relief. 4, 5

Critical pitfall: The swelling is caused by allergic inflammation, NOT infection—antibiotics are not indicated unless there is evidence of secondary infection (progressive redness, increasing pain, purulent discharge, fever), which is uncommon. 1, 5

Simple Local Reactions

Most insect stings cause mild, self-limited local reactions requiring minimal or no treatment. 1, 5

• Remove stinger immediately (within 10-20 seconds) by scraping or flicking with a fingernail—never grasp and pull the venom sac as this injects more venom. 2, 4
• Wash area with soap and water. 2
• Apply ice or cold packs to reduce pain and swelling. 2, 5
• Take over-the-counter oral antihistamines to alleviate itching. 2, 5
• Apply topical corticosteroids to reduce itching. 2

Post-Acute Management and Prevention

For Patients with Systemic Reactions

All patients who experience systemic reactions require:

• Prescription of epinephrine autoinjector for emergency self-treatment with education on proper use and indications for administration. 2, 4
• Referral to allergist-immunologist for venom-specific IgE testing (skin testing starting at 0.001-0.01 mg/mL intracutaneous, increasing by 10-fold increments to maximum 1.0 mg/mL). 1, 2, 4
• Consideration of venom immunotherapy (VIT), which can reduce the 25-70% risk of future systemic reactions to nearly zero. 1

For Patients with Large Local Reactions

• Optional prescription of injectable epinephrine for use if systemic reaction occurs in the future, though most patients need only symptomatic care. 1
• Consider VIT for patients with unavoidable, frequent large local reactions and detectable venom-specific IgE, as growing evidence shows VIT significantly reduces size and duration of these reactions. 1

Special Considerations

• Eye stings (to the eye itself, not just eyelid) require immediate medical evaluation due to risk of permanent vision loss. 2
• Multiple stings (typically >100) can cause toxic reactions from massive envenomation even in non-allergic individuals, potentially causing multi-organ dysfunction. 2, 4
• Fire ant stings produce a pathognomonic sterile pseudopustule within 24 hours—leave intact and keep clean to prevent secondary infection. 1
• Delayed reactions (serum sickness, vasculitis) occurring 1-2 weeks after stings are rare but possible and are still IgE-mediated; VIT is recommended for these patients. 6

Prevention Strategies

• Have known nests removed by professionals. 2
• Avoid bright clothing, flowery prints, and scented products. 2, 5
• Wear protective clothing and avoid walking barefoot near water and vegetation. 2
• Be cautious near bushes, eaves, garbage containers, and picnic areas. 2
• Avoid eating or drinking outdoors when possible. 2