What are the evidence‑based guidelines for managing insect bites, including first‑aid measures, pharmacologic treatment, antibiotic use, tetanus prophylaxis, and management of systemic allergic reactions?

Insect Bite Management Guidelines

Immediate Management of Local Reactions

For simple local reactions (redness, swelling, itching, pain resolving within 24 hours), apply cold compresses, administer oral antihistamines such as cetirizine for pruritus, and use oral analgesics like acetaminophen or ibuprofen for pain relief. 1, 2

• Cold compresses reduce local pain and swelling effectively 1, 3
• Oral antihistamines (e.g., cetirizine) are preferred due to minimal sedation 1, 2
• Antibiotics are not indicated for simple local reactions unless clear secondary bacterial infection is evident—swelling results from mediator release, not infection 1, 2

Large Local Reactions (>10 cm, lasting 5-10 days)

• Continue cold compresses and oral antihistamines 1
• Oral corticosteroids may be considered if initiated within 24-48 hours for severe cases, though definitive controlled-trial evidence is lacking 1, 2, 3
• Up to 10% of patients with large local reactions may later develop systemic reactions; prescribing an epinephrine autoinjector is reasonable in this group 1
• Venom-specific IgE testing and venom immunotherapy (VIT) are generally not indicated unless the patient has frequent unavoidable exposure and demonstrable venom-specific IgE 1

Systemic Reactions and Anaphylaxis Management

Administer intramuscular epinephrine immediately as first-line therapy: 0.3-0.5 mg in adults, 0.01 mg/kg (maximum 0.3 mg) in children, injected into the anterolateral thigh. 1, 2, 3

• Intramuscular injection in the thigh achieves faster and higher plasma epinephrine concentrations than subcutaneous or arm injection 1
• Repeat epinephrine dosing may be required for persistent or recurrent symptoms 1
• No absolute contraindication exists even in patients with hypertension, cardiac arrhythmias, or β-blocker therapy—the risk of untreated anaphylaxis outweighs potential cardiac effects 1
• Delayed epinephrine administration is associated with fatal outcomes 1, 2, 3
• Transport to emergency department for further evaluation and supportive therapy 3, 4

Post-Acute Care and Prevention

All patients who experience systemic reactions must receive a prescription for an epinephrine autoinjector and carry it at all times. 1, 2, 3

• Provide structured training on proper autoinjector technique and indications for self-administration 1
• Recommend a medical identification bracelet or necklace indicating allergy to insect stings 1
• Refer to an allergist-immunologist for venom-specific IgE testing (skin testing preferred over in-vitro for initial evaluation) and evaluation for venom immunotherapy 5, 1, 2
• If skin testing is negative after a convincing anaphylactic episode, perform in-vitro IgE testing or repeat skin testing after ≥6 weeks, as tests can be temporarily non-reactive 1, 2

Venom Immunotherapy (VIT) Indications and Protocol

VIT is indicated for adults with any systemic reaction beyond isolated cutaneous signs, and for children with systemic reactions involving respiratory or cardiovascular symptoms. 5, 1, 2

• VIT reduces the risk of subsequent systemic reactions to <5%, and reactions that occur during therapy are generally milder than pre-treatment reactions 1, 2
• VIT can prevent death from subsequent stings in hypersensitive patients 5
• Recommended duration is 3-5 years; 80-90% of patients remain free of systemic reactions after discontinuation 1, 2
• Extended or indefinite VIT is advised for individuals with severe anaphylaxis featuring shock or loss of consciousness 1
• Maintenance dose intervals can be increased to 4-week intervals during the first year and eventually to every 6-12 weeks 5
• VIT may be considered for adults with only cutaneous systemic manifestations, though this remains somewhat controversial 1

Medication Interactions and Risk Factors

• β-adrenergic blocking agents increase the risk of severe anaphylaxis to stings and to VIT; discontinue when feasible 1
• ACE inhibitors are associated with higher risk of severe anaphylaxis (odds ratio ≈2.27); consider alternative antihypertensives when appropriate 1
• If these medications cannot be stopped, VIT decisions should be individualized, but for patients with life-threatening sting reactions, the benefit of VIT generally outweighs medication-related risk 1
• Mastocytosis is found in 3-5% of patients with sting anaphylaxis, rendering these patients prone to very severe reactions 6

Insect Avoidance Strategies

• Have nests of stinging insects removed by trained professionals from the home environment 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, 3
• Refrain from walking barefoot or in open footwear such as sandals 1
• Exercise caution near bushes, eaves, attics, garbage containers, and picnic areas 1
• Keep insecticides readily available for killing stinging insects from a distance (note: repellents are ineffective against stinging insects) 1
• Avoid eating or drinking outdoors and use caution with opaque containers and straws 1

Mosquito-Specific Prevention

• Use insect repellents containing DEET on exposed skin—the most effective mosquito repellent available 3
• Apply DEET-containing repellents sparingly to exposed skin or clothing; avoid high-concentration products on skin, particularly on children 3
• Use permethrin (Permanone) on clothing for additional protection 3
• Stay in well-screened areas and use mosquito nets when sleeping in endemic areas 3
• Use pyrethrum-containing flying-insect spray in living and sleeping areas during evening hours 3

Tetanus Prophylaxis

While the provided evidence does not specifically address tetanus prophylaxis for insect bites, standard wound care principles apply: ensure tetanus immunization is up to date per CDC guidelines (booster if >10 years since last dose, or >5 years for contaminated wounds).

Common Pitfalls to Avoid

• Do not prescribe antibiotics for local swelling without evidence of secondary infection—this is ineffective and contributes to antibiotic resistance 1, 2
• Do not delay epinephrine in systemic reactions—this is associated with fatal outcomes 1, 2
• Do not perform skin testing within 6 weeks of reaction, as results may be falsely negative 1, 2
• Patient identification of specific insect species is frequently incorrect; allergy testing and history-test correlation are needed for accurate identification 5
• Among patients with positive venom-specific IgE, 30-60% (not 100%) will experience a systemic reaction if re-stung 1
• Large local swelling should not be mistaken for infection 1