How should an insect bite allergy be managed?

Treatment of Insect Bite Allergy

For local reactions, use cold compresses and oral antihistamines; for systemic reactions, immediately administer intramuscular epinephrine 0.3-0.5 mg in adults (0.01 mg/kg up to 0.3 mg in children) in the anterolateral thigh, as delayed epinephrine is associated with fatal outcomes. 1, 2

Immediate Management Based on Reaction Severity

Simple Local Reactions

Most insect bites cause only localized redness, swelling, itching, and pain that resolve within 24 hours and require minimal intervention. 1

• Apply cold compresses to reduce local pain and swelling 1, 2
• Give oral antihistamines (such as cetirizine for minimal sedation) to reduce itching and discomfort 1, 2
• Provide oral analgesics (acetaminophen or ibuprofen) for pain relief 1
• Do NOT prescribe antibiotics unless clear signs of secondary bacterial infection develop—the swelling is from mediator release, not infection 1, 3

Large Local Reactions

These reactions increase in size over 24-48 hours, extend more than 10 cm from the sting site, and take 5-10 days to resolve. 1

• Initiate oral corticosteroids promptly (within the first 24-48 hours) for severe cases to limit progression, though definitive controlled trial evidence is lacking 1, 3, 4
• Continue cold compresses and oral antihistamines 1, 2
• Consider prescribing an epinephrine autoinjector (optional but reasonable) since up to 10% of patients with large local reactions may eventually experience systemic reactions 1
• These patients are generally NOT candidates for venom-specific IgE testing or venom immunotherapy (VIT) unless they have frequent, unavoidable exposures and detectable venom-specific IgE 1

Systemic Reactions/Anaphylaxis

Systemic symptoms include urticaria/angioedema not contiguous with the sting site, respiratory symptoms (dyspnea, wheeze, upper airway swelling), cardiovascular symptoms (hypotension, shock, arrhythmias), gastrointestinal symptoms (nausea, vomiting, diarrhea), or neurological symptoms. 1

• Administer intramuscular epinephrine IMMEDIATELY as the first-line treatment—0.3-0.5 mg in adults, 0.01 mg/kg (maximum 0.3 mg) in children, injected into the anterolateral thigh 1, 2, 5
• Intramuscular injection in the thigh achieves more rapid and higher plasma concentrations than subcutaneous or arm injection 1
• Repeat dosing may be required for persistent or recurrent symptoms 1
• There is NO contraindication to epinephrine in life-threatening anaphylaxis, even in patients with hypertension, cardiac arrhythmias, or those taking β-blockers—the risk of anaphylaxis exceeds the risk of epinephrine's cardiac effects 1, 2
• Antihistamines and corticosteroids are NOT substitutes for epinephrine in anaphylaxis 3

Post-Acute Management and Prevention

For All Patients with Systemic Reactions

All patients who experience systemic reactions must receive the following: 1, 2

• Prescription for an epinephrine autoinjector to carry at all times 1, 2, 3
• Training on proper use and indications for self-administration 1
• Referral to an allergist-immunologist for venom-specific IgE testing (skin testing or in vitro assay) and consideration of VIT 1, 2, 3
• Education on insect avoidance measures (detailed below) 1
• Consider obtaining a medical identification bracelet or necklace 1

Venom Immunotherapy (VIT)

VIT is highly effective and should be strongly considered for appropriate candidates. 1, 2

• VIT reduces the risk of subsequent systemic reactions to less than 5%, and any reactions that occur during VIT are usually milder than pre-treatment reactions 1, 2
• Indications for VIT: Adults with any systemic reaction beyond isolated cutaneous manifestations; children with systemic reactions involving respiratory or cardiovascular symptoms 1
• VIT is controversial but usually recommended for adults with only cutaneous systemic manifestations 1
• Testing considerations: If skin tests are negative despite convincing anaphylaxis history (especially with severe symptoms like upper airway obstruction or hypotension), perform in vitro IgE testing or repeat skin testing in 6 weeks, as tests may be temporarily non-reactive immediately after a reaction 1
• Duration: VIT should usually continue for 3-5 years, with 80-90% of patients not experiencing systemic reactions after discontinuation 1
• Extended or indefinite VIT may be warranted for patients with history of severe anaphylaxis with shock or loss of consciousness 1, 2

Insect Avoidance Measures

Educate patients on the following strategies: 1

• Have nests removed by trained professionals from the immediate vicinity of the home 1
• Avoid brightly colored clothing, flowery prints, and strongly scented materials that attract insects 1
• Wear long pants, long-sleeved shirts, socks, closed shoes, and work gloves when outdoors 1
• Avoid walking barefoot or in open shoes (sandals) 1
• Be cautious near bushes, eaves, attics, garbage containers, and picnic areas 1
• Keep insecticides readily available for killing stinging insects from a distance (note: insect repellents do NOT work on stinging insects) 1
• Avoid eating or drinking outdoors, and use caution with opaque containers and straws 1

Special Considerations and Pitfalls

Medication Interactions

• Patients taking β-adrenergic blocking agents are at greater risk for severe anaphylaxis to both stings and VIT; these medications should be discontinued if possible 1
• Angiotensin-converting enzyme (ACE) inhibitors are associated with increased risk of severe anaphylaxis (odds ratio 2.27); consider alternatives if equally effective options exist 1
• If these medications cannot be discontinued, VIT decisions should be individualized, but for patients with life-threatening sting reactions, the risk of VIT is generally less than the risk of future stings 1

Common Diagnostic Pitfalls

• Do not confuse large local swelling with infection—antibiotics are not indicated unless secondary infection is clearly present 1, 3
• Approximately 30-60% of patients with positive venom-specific IgE will experience systemic reactions if re-stung, not 100% 1
• Rarely (<1%), patients can have anaphylaxis despite negative skin and in vitro tests; some may have underlying systemic mastocytosis 1

Mosquito Bites

While most evidence focuses on stinging insects (bees, wasps, fire ants), mosquito bites typically cause only local reactions mediated by IgE antibodies to mosquito saliva proteins. 6, 7

• Cetirizine is effective against mosquito bite whealing and pruritus 6, 7
• Systemic reactions to mosquito bites are very rare 6, 7