What is the management for a patient with an insect sting, considering potential allergic reactions and history of severe allergies?

Management of Insect Sting Reactions

For any systemic reaction to an insect sting, immediately administer intramuscular epinephrine 0.3-0.5 mg in adults (0.01 mg/kg up to 0.3 mg in children, 0.5 mg in teenagers) into the anterolateral thigh and activate emergency medical services—this single intervention is the most critical life-saving action. 1, 2, 3

Immediate Assessment and Classification

Local Reactions

• Most insect stings cause only transient local reactions with redness, swelling, itching, and pain that resolve within hours to days 4
• Large local reactions are defined by swelling >10 cm in diameter contiguous to the sting site, increasing in size for 24-48 hours, and taking 5-10 days to resolve 4
• These reactions are IgE-mediated but self-limited and rarely create serious health problems 4

Systemic Reactions

Systemic reactions include manifestations not contiguous with the sting site and range from mild to life-threatening 4:

• Cutaneous: urticaria and angioedema beyond the sting site
• Respiratory: bronchospasm, upper airway obstruction (tongue/throat swelling, laryngeal edema)
• Cardiovascular: hypotension, shock, arrhythmias, coronary artery spasm
• Gastrointestinal: nausea, vomiting, diarrhea, abdominal pain
• Neurological: seizures

Laryngeal edema is the most common cause of death from Hymenoptera-induced anaphylaxis 1

Acute Management Algorithm

For Local Reactions Only

• Remove the stinger immediately by scraping or flicking it away with a fingernail or tweezers 1
• Apply cold compresses to reduce local pain and swelling 4
• Administer oral antihistamines and analgesics for itching or pain 4
• For severe large local reactions, consider a short course of oral corticosteroids (though definitive proof of efficacy through controlled studies is lacking) 4
• Antibiotics are NOT indicated unless there is evidence of secondary infection—the swelling is caused by allergic inflammation, not infection 4

For Systemic Reactions (Anaphylaxis)

Step 1: Epinephrine Administration

• Inject epinephrine intramuscularly in the mid-outer thigh (vastus lateralis muscle) immediately upon recognition of anaphylaxis 1, 2, 3
• Adult dose: 0.3-0.5 mg depending on reaction severity 1, 5
• Pediatric dose: 0.01 mg/kg (maximum 0.3 mg in prepubertal children, up to 0.5 mg in teenagers) 1, 2
• Intramuscular injection in the anterolateral thigh achieves faster and higher plasma concentrations than subcutaneous or arm injections 1
• Be prepared to repeat epinephrine every 5-15 minutes if symptoms persist or worsen 1, 2
• Fatal sting reactions are consistently associated with delayed or absent epinephrine administration 4, 1, 2

Step 2: Immediate Supportive Measures

• Call emergency services immediately after administering epinephrine, without delay 1, 3
• Position the patient supine with legs elevated if hypotension develops to prevent sudden death from "empty-ventricle syndrome" 1
• Remove the stinger immediately to prevent additional venom injection 1

Step 3: Additional Interventions

• Administer 1-2 liters of IV normal saline bolus for persistent hypotension, as massive fluid shifts occur during anaphylaxis 1
• For refractory hypotension despite multiple IM doses, transition to intravenous epinephrine infusion 1
• Provide supplemental oxygen to all patients with prolonged reactions, hypoxemia, or requiring multiple epinephrine doses 1, 3
• Administer inhaled albuterol (2.5 mg nebulized) for bronchospasm that persists despite epinephrine 1

Step 4: Adjunctive Therapy (AFTER Epinephrine)

• H1 antihistamines: diphenhydramine 1-2 mg/kg IV (maximum 50 mg) at a rate not exceeding 25 mg/min—but this does NOT treat life-threatening symptoms 1, 2
• H2 blockers: ranitidine 50 mg IV or famotidine 20 mg IV 1
• Corticosteroids: methylprednisolone 125 mg IV or prednisone 0.5 mg/kg PO to potentially prevent biphasic reactions, though they have no immediate effect 1
• Critical caveat: Antihistamines and corticosteroids cannot substitute for epinephrine in life-threatening reactions 2

Step 5: Observation

• Observe patients for 4-6 hours minimum for biphasic reactions (longer if severe initial reaction) 2

Discharge and Prevention

Prescription Requirements

• Prescribe an epinephrine autoinjector (EpiPen or equivalent) before discharge and demonstrate proper use 1, 2, 3
• Because some patients may require more than one injection, prescription of more than one epinephrine injector should be considered 4
• Continue diphenhydramine every 6 hours for 2-3 days post-discharge 2
• Add an H2 antihistamine (such as ranitidine) and corticosteroid (such as prednisone) for 2-3 days 2

Mandatory Referral

• Refer ALL patients with systemic reactions to an allergist-immunologist for venom-specific IgE testing and consideration of venom immunotherapy (VIT) 1, 2, 3
• Consultation with an allergist is recommended to determine the degree of risk and the most suitable approach to prevent a systemic reaction 4

Risk Stratification for Future Reactions

• Patients with previous large local reactions have a 5-10% risk of systemic reactions to future stings 4, 6
• Patients with previous systemic reactions have a 25-70% risk of future systemic reactions, depending on the severity of previous reactions 4, 6
• VIT reduces this risk to less than 5% and is extremely effective 4, 3

Venom Immunotherapy Indications

VIT is indicated for:

• Adults with a history of systemic reactions beyond isolated cutaneous manifestations 4, 3
• Children with systemic reactions involving respiratory, cardiovascular, or other non-cutaneous manifestations 4
• VIT is generally NOT necessary in children ≤16 years who have experienced isolated cutaneous systemic reactions without other systemic manifestations 4
• VIT in adults with only cutaneous manifestations is controversial but usually recommended 4

VIT duration:

• Continue for at least 3-5 years in most patients 4, 3
• 80-90% of patients will not have a systemic reaction if VIT is stopped after 3-5 years 4
• Consider extended duration (possibly indefinitely) in patients with history of severe anaphylaxis with shock or loss of consciousness 4

Avoidance Education

• Avoid walking barefoot outdoors 1, 3
• Wear protective clothing 1, 3
• Avoid bright colors and floral patterns 1
• Eliminate scented products 1, 3
• Have nests professionally removed 1

Special Populations at Higher Risk

Factors Associated with Higher Risk of Severe Reactions

• History of extreme or near-fatal reactions to stings 4
• Systemic reactions during VIT (to an injection or a sting) 4
• Severe honeybee allergy 4
• Coexisting asthma (especially if severe or poorly controlled) 1
• Adolescence (associated with higher fatality rates) 1
• Older age and cardiovascular disease 1
• Underlying medical conditions or frequent unavoidable exposure 4

Patients on Beta-Blockers

• Although patients with coexisting conditions such as hypertension or cardiac arrhythmias, or concomitant medications such as β-adrenergic blocking agents, may require special attention, there is no contraindication to the use of epinephrine in a life-threatening situation such as anaphylaxis 4

Common Pitfalls to Avoid

• Never delay epinephrine administration—delay is strongly associated with fatal outcomes 4, 1, 2
• Never substitute antihistamines for epinephrine in systemic reactions—diphenhydramine is never a substitute for epinephrine 2
• Do not prescribe antibiotics for large local reactions unless there is evidence of secondary infection 4
• Do not confuse fire ant pseudopustules with infection—the sterile pseudopustule that develops within 24 hours is pathognomonic of fire ant stings and should be left intact 4
• Do not fail to prescribe epinephrine autoinjectors to patients with systemic reactions—this is mandatory 1, 2, 3
• Do not fail to refer patients with systemic reactions to an allergist—VIT can reduce future reaction risk from 25-70% to nearly zero 1, 3