What is the treatment for a patient with a history of severe food allergies experiencing an allergic reaction to lo mein?

Treatment for Allergic Reaction to Lo Mein

Administer intramuscular epinephrine immediately into the anterolateral thigh (0.3-0.5 mg for adults, 0.01 mg/kg up to 0.3 mg for children) as first-line treatment if the patient exhibits any respiratory symptoms, tongue swelling, hypotension, or multi-system involvement—antihistamines alone are never appropriate for anaphylaxis and delay in epinephrine administration has been associated with fatal outcomes. 1

Immediate Management Algorithm

First-Line Treatment: Epinephrine

• Epinephrine is the only appropriate first-line treatment for food-induced anaphylaxis and must not be delayed to administer antihistamines 2, 1
• Administer intramuscularly in the anterolateral thigh (vastus lateralis), which produces the most rapid rise in serum levels 3
• Adult dose: 0.3-0.5 mg IM 1
• Pediatric dose: 0.01 mg/kg (maximum 0.3 mg) IM 1
• Fatal reactions are specifically associated with delayed epinephrine administration 1
• Patients with any history of respiratory symptoms or hypotension during previous food reactions should receive epinephrine immediately 2

Supportive Care

• For hypotension or significant vomiting: administer IV fluid bolus with Ringer's lactate 10-20 mL/kg 1
• Position patient supine with legs elevated to improve venous return 4
• Monitor blood pressure frequently as individual response to epinephrine varies significantly 5

Second-Line Adjunctive Treatments (Only After Epinephrine)

Antihistamines

• H1 antihistamine: Diphenhydramine 25-50 mg IV/oral (adults) or 1-2 mg/kg (children); alternatively cetirizine 10 mg for adults 1
• H2 antihistamine: Ranitidine 1-2 mg/kg per dose (maximum 75-150 mg) or famotidine, used in combination with H1 antihistamines 1
• Continue H1 antihistamine every 6 hours for 2-3 days post-discharge 2
• Continue H2 antihistamine twice daily for 2-3 days post-discharge 2

Corticosteroids

• Prednisone 1 mg/kg (maximum 60-80 mg) orally to prevent biphasic or protracted reactions 1
• Continue daily for 2-3 days after discharge 2
• Important caveat: Little data actually support corticosteroid use for preventing biphasic reactions, but they are commonly recommended due to anti-inflammatory properties 2

Observation and Monitoring

Duration of Observation

• Observe for 4-6 hours minimum after symptom resolution, or longer based on reaction severity 2, 1
• Patients with minimal symptoms (few hives that resolved promptly) may be discharged after 2 hours if physician assesses minimal risk of progression 2
• Biphasic reactions can occur up to 6 hours after initial symptoms, necessitating extended monitoring 2
• Patients with history of severe biphasic reactions require longer observation even without symptoms 2

Transport Requirements

• After epinephrine administration, transport patient to emergency facility by ambulance for monitoring 2
• This applies even if symptoms appear to resolve, due to biphasic reaction risk 1

Identifying the Culprit Allergen in Lo Mein

Lo mein commonly contains multiple potential allergens that require investigation:

• Shellfish (shrimp, crab) - common cross-reactivity among various shellfish 2
• Peanuts or tree nuts (peanut oil, cashews in sauce) - associated with severe or fatal reactions 4
• Soy (soy sauce, tofu)
• Wheat (noodles)
• Eggs (sometimes in noodles)
• Sesame (sesame oil)

Patients should be educated about cross-reactivity, particularly among shellfish varieties 2

Discharge Planning and Long-Term Management

Mandatory Prescriptions

• Prescribe epinephrine auto-injector (2 doses) with proper training on use 1
• Patients must understand epinephrine should be available at all times—compliance is most difficult in adolescents and young adults 2
• Provide oral antihistamines and corticosteroids for continuation therapy 2

Patient Education Requirements

• Allergen avoidance strategies: teach effective label reading and restaurant ingredient inquiry 2
• Early recognition of anaphylaxis signs and symptoms 2
• Anaphylaxis emergency action plan implementation 2
• Medical identification jewelry or anaphylaxis wallet card 2
• Restaurant exposure constitutes special hazard for food allergy patients 2

Follow-Up

• Arrange follow-up with primary care provider after the reaction 2
• Refer to allergist/immunologist for proper allergen identification and long-term management 1, 4
• Patients should report all anaphylactic reactions to physician as soon as possible to help define specific food causing reaction 2

Critical Pitfalls to Avoid

• Never use antihistamines as primary treatment instead of epinephrine for severe reactions—this is the most common reason for not using epinephrine and significantly increases risk of life-threatening progression 2, 1
• Do not delay epinephrine to administer other medications 1
• Do not inject epinephrine into buttocks, digits, hands, or feet—only anterolateral thigh 1
• Do not discharge patients too early without adequate observation for biphasic reactions 1
• Avoid misdiagnosing angioedema as infection and inappropriately prescribing antibiotics 1

Special Considerations

Patients on Beta-Blockers

• Glucagon should be available as additional treatment option 1
• For refractory hypotension: glucagon 20-30 μg/kg (children) or 1-5 mg (adults) 1

Refractory Anaphylaxis

• Repeated epinephrine doses may be needed 2
• IV fluids, corticosteroids, and vasopressor agents may be required 2
• Prompt transfer to intensive care unit is essential 2