What are the recommended pharmacologic treatments for a typical insect bite?

Pharmacologic Treatment for Typical Insect Bites

For simple insect bites, use oral antihistamines (such as cetirizine) and cold compresses as first-line treatment; reserve antibiotics only for clear signs of secondary bacterial infection, and never delay epinephrine if any systemic symptoms develop. 1, 2

Simple Local Reactions (Most Common Presentation)

First-line symptomatic treatment:

• Oral antihistamines (e.g., cetirizine) to reduce itching, pain, and inflammation—this is the primary pharmacologic intervention recommended by the American Academy of Allergy, Asthma, and Immunology 1, 2, 3
• Oral analgesics (acetaminophen or ibuprofen) for pain relief 1, 2
• Cold compresses as adjunctive non-pharmacologic therapy 1, 2

Critical pitfall: Simple local reactions resolve within 24 hours and are caused by allergic mediator release, not infection—antibiotics are inappropriate and contribute to antimicrobial resistance 2, 4

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

Escalated pharmacologic approach:

• Continue oral antihistamines and cold compresses 1, 2
• Oral corticosteroids initiated within the first 24-48 hours for severe cases with extensive swelling, though controlled trial evidence is limited 1, 2, 5
• Elevate the affected limb if swelling is significant 2

Important caveat: These reactions are IgE-mediated allergic inflammation, not infection. Antibiotics should only be prescribed when clear signs of secondary bacterial infection appear: progressive redness, increasing pain, purulent discharge, fever, or warmth and tenderness 1, 2

Systemic Reactions (Life-Threatening Emergency)

Immediate life-saving pharmacotherapy:

• Intramuscular epinephrine 0.3-0.5 mg in adults (0.01 mg/kg, max 0.3 mg in children) injected into the anterolateral thigh—this is the only first-line treatment for anaphylaxis 1, 6
• Repeat dosing may be required for persistent or recurrent symptoms 1
• Intramuscular thigh injection achieves faster and higher plasma concentrations than subcutaneous or arm injection 1

Critical warning: Antihistamines and corticosteroids are NOT substitutes for epinephrine in anaphylaxis. Delayed epinephrine administration is associated with fatal outcomes 1, 5. There is no absolute contraindication to epinephrine even in patients with hypertension, cardiac arrhythmias, or β-blocker therapy—the risk of untreated anaphylaxis outweighs potential cardiac effects 1

Post-Acute Management for At-Risk Patients

Essential prescriptions:

• Epinephrine autoinjector for lifelong carry-by use in any patient who experienced systemic reactions or severe large local reactions 1, 2, 5
• Consider prescribing more than one autoinjector, as some patients may require multiple doses 1

Referral pathway: All patients with systemic reactions (including widespread urticaria or angioedema) should be referred to an allergist-immunologist for venom-specific IgE testing and evaluation for venom immunotherapy (VIT), which reduces subsequent systemic reaction risk to <5% 1, 2, 5

What NOT to Prescribe

Avoid these common errors:

• No routine antibiotics for simple or large local reactions—the swelling is allergic inflammation, not infection 1, 2, 4
• Antibiotics contribute to antimicrobial resistance and are overused in insect bite management, accounting for up to 10.7% of flucloxacillin prescriptions during peak summer months 4
• Fire ant stings produce sterile pseudopustules within 24 hours that are pathognomonic and not infected 2