What is the treatment for a 40-year-old female with facial swelling, itching on ears, and possible anaphylaxis after a suspected insect sting or bite while swimming?

Immediate Management of Suspected Insect Sting with Allergic Reaction

Administer intramuscular epinephrine 0.3-0.5 mg immediately into the anterolateral thigh and activate emergency medical services (EMS) now—this patient has facial swelling and itching consistent with a systemic allergic reaction to an insect sting, and delayed epinephrine administration is associated with fatal outcomes. 1, 2

Immediate Treatment Protocol

Epinephrine is the only first-line treatment for systemic reactions:

• Administer 0.3-0.5 mg intramuscular epinephrine in the anterolateral thigh immediately (this achieves faster and higher plasma concentrations than subcutaneous or arm injections) 1, 2
• Call 911/activate EMS immediately after epinephrine administration 2
• Be prepared to repeat the epinephrine dose in 10-20 minutes if symptoms persist or worsen 1
• Place the patient in a recumbent position with legs elevated if any signs of hypotension develop 1

Critical pitfall: Antihistamines and corticosteroids are NOT substitutes for epinephrine and should only be considered AFTER epinephrine administration 1, 3

Clinical Assessment

This presentation suggests a systemic allergic reaction because:

• Facial swelling (angioedema) extending beyond the sting site indicates systemic involvement 1
• Itching on ears (remote from presumed sting site) suggests generalized urticaria or systemic mediator release 4, 5
• Aquatic environment exposure suggests possible jellyfish, water insect, or other stinging organism 1

Monitor closely for progression to anaphylaxis:

• Difficulty breathing, wheezing, or throat tightness (airway compromise) 4, 5
• Lightheadedness, syncope, or hypotension (cardiovascular compromise) 4, 6
• Widespread urticaria, tongue swelling, or worsening facial edema 2, 5
• Vomiting, diarrhea, or abdominal cramping (gastrointestinal symptoms) 4

Adjunctive Treatments (ONLY After Epinephrine)

Once epinephrine is administered and EMS activated:

• Oral antihistamines (H1 antagonist like diphenhydramine) may help reduce itching but will have minimal immediate effect on life-threatening symptoms 1, 2
• Consider H2 antagonist (like ranitidine or famotidine) as adjunct therapy 5, 6
• Oral corticosteroids may be considered to prevent biphasic reactions, though they have no immediate effect 1, 5
• Maintain airway and provide oxygen if respiratory symptoms develop 1, 6

Observation and Disposition

This patient requires emergency department evaluation:

• Observe for 4-12 hours minimum for potential biphasic reactions (recurrence of symptoms without re-exposure) 5, 6
• Biphasic reactions can occur in severe anaphylaxis, though the exact frequency after insect stings is uncertain 1
• Do not discharge from urgent care—transfer to emergency department for monitoring 6

Post-Acute Management

Before discharge from the emergency department:

• Prescribe epinephrine autoinjector (two doses) for emergency self-treatment 1, 2
• Provide education on autoinjector use and indications for administration 1
• Refer to allergist-immunologist for venom-specific IgE testing and consideration of venom immunotherapy (VIT) 1
• Recommend medical identification bracelet indicating insect sting allergy 1

Avoidance Education

Counsel on prevention strategies:

• Avoid walking barefoot or in open shoes near water and vegetation 1
• Wear protective clothing (long sleeves, pants) during outdoor activities 1, 2
• Avoid brightly colored clothing and scented products that attract insects 1, 2
• Have nests near home removed by professionals 1, 2
• Keep insecticides for stinging insects readily available 1

Key clinical pearl: Even if symptoms appear mild initially, systemic reactions can rapidly progress to life-threatening anaphylaxis—when in doubt, administer epinephrine, as it is safer to give epinephrine unnecessarily than to delay administration 7, 6