What medication is recommended for a patient experiencing an allergic reaction, considering the severity of the reaction and potential history of severe allergic reactions?

Medication for Allergic Reactions

Epinephrine is the first-line medication for any allergic reaction involving more than just isolated mild skin symptoms, and should be administered immediately without delay when a patient experiences symptoms after known allergen exposure or when anaphylaxis is suspected. 1, 2

Immediate Treatment Algorithm

Epinephrine Administration (First-Line)

When to administer epinephrine:

• Any allergic reaction involving two or more organ systems 3
• Generalized urticaria after known allergen exposure (e.g., food, drug, insect sting) 1
• Any respiratory symptoms (wheezing, throat tightness, difficulty breathing) 2
• Any cardiovascular symptoms (hypotension, dizziness, syncope) 2
• Key principle: err on the side of giving epinephrine rather than waiting 1

Dosing:

• Adults and children ≥30 kg: 0.3 mg intramuscular into anterolateral thigh 2
• Children 10-25 kg: 0.15 mg intramuscular into anterolateral thigh 2
• Alternative dosing: 0.01 mg/kg (maximum 0.5 mg per dose) using 1:1,000 solution 2
• Repeat every 5-15 minutes if symptoms persist or progress 1, 2

Route: Intramuscular injection into the anterolateral thigh is the preferred route; this is more effective than subcutaneous administration 4

Adjunctive Medications (Second-Line, Given WITH Epinephrine)

H1-Antihistamine (Diphenhydramine):

• Dose: 1-2 mg/kg per dose (maximum 50 mg) IV or oral 1, 2
• Provides symptomatic relief of urticaria and pruritus 2
• Critical: Never delays or replaces epinephrine 2
• FDA-approved for amelioration of allergic reactions as adjunct to epinephrine after acute symptoms are controlled 5

H2-Antihistamine (Ranitidine or Famotidine):

• Add as adjunctive therapy, particularly for urticaria 1, 2
• Combination of H1 + H2 antihistamines more effective than H1 alone for urticaria relief 6
• Continue for 2-3 days post-discharge to help prevent biphasic reactions 2

Bronchodilators (Albuterol):

• Only if wheezing or bronchospasm present 2
• Dose: 4-8 puffs (child) or 8 puffs (adult) via MDI, or continuous nebulization 2

Supplemental Oxygen:

• Administer for any respiratory distress 2

IV Fluids:

• Large volume boluses (10-20 mL/kg) for orthostasis, hypotension, or incomplete response to epinephrine 1, 2
• Ringer's lactate or normal saline, repeated as needed 1

Severity-Based Treatment Approach

Mild Reactions (Isolated Skin Symptoms Only)

If only a few hives with no other symptoms:

• Consider epinephrine if exposure to known allergen, as progression can occur 1
• Minimum: oral antihistamine (diphenhydramine) 3
• However, if any doubt exists about progression, give epinephrine 1

Moderate to Severe Reactions

Any of the following mandate immediate epinephrine:

• Generalized urticaria 1
• Angioedema 1
• Respiratory symptoms (dyspnea, wheezing, throat tightness) 7
• Gastrointestinal symptoms (nausea, vomiting, abdominal pain) after allergen exposure 7
• Cardiovascular changes (hypotension, tachycardia) 7

Treatment sequence:

1. Epinephrine IM immediately 2
2. Place patient recumbent with legs elevated 1
3. Administer H1-antihistamine (diphenhydramine) 2
4. Add H2-antihistamine 2
5. Bronchodilator if wheezing 2
6. IV fluids if hypotensive 2
7. Supplemental oxygen 2

Life-Threatening Anaphylaxis

Characterized by:

• Acute onset with generalized hives, respiratory compromise, severe hypotension 7
• Cardiovascular shock 3
• Cardiac or respiratory arrest 3

Treatment:

• Immediate epinephrine IM, repeat every 5-15 minutes as needed 2
• Aggressive IV fluid resuscitation 2
• Consider continuous IV epinephrine infusion for refractory hypotension 2
• Full ACLS protocols if cardiac arrest 7

Critical Post-Treatment Management

Observation Period:

• Minimum 4-6 hours for all patients receiving epinephrine 1, 2
• Extend to 12 hours if: severe initial reaction, history of biphasic reactions, delayed epinephrine administration, or ongoing symptoms 2
• Biphasic reactions can occur up to 6 hours after initial reaction 7

Discharge Requirements:

• Prescribe two epinephrine auto-injectors with hands-on training 2
• Written anaphylaxis emergency action plan 2
• Continue H1 and H2 antihistamines for 2-3 days 2
• Medical identification jewelry or wallet card 2
• Follow-up with allergist/immunologist 2

Common Pitfalls to Avoid

Reluctance to use epinephrine:

• Serious adverse effects are rare in otherwise healthy individuals 1, 2
• Common effects (pallor, tremor, anxiety, palpitations) are transient and expected 1
• Delayed epinephrine administration contributes to fatalities 1

Relying solely on antihistamines:

• Antihistamines do NOT reverse life-threatening cardiovascular or respiratory manifestations 2
• They provide only symptomatic relief of urticaria and pruritus 2

Inappropriate use of corticosteroids:

• No evidence that corticosteroids prevent or reduce severity of acute anaphylaxis 7
• Should not be used indiscriminately, especially in immunocompromised patients 7
• No role in immediate treatment of allergic reactions 7

Premature discharge:

• All patients receiving epinephrine must be transferred to emergency facility for observation 1
• Never discharge before minimum observation period completed 2

Special Populations

Patients on beta-blockers:

• May have reduced response to epinephrine 2
• Have glucagon readily available 2
• Epinephrine still indicated; serious adverse effects remain rare 2

Patients with cardiovascular disease:

• Epinephrine still indicated 2
• Benefits exceed risks when dosed appropriately 4
• Properly administered epinephrine has no absolute contraindication in anaphylaxis 4