What is the dose of Avil (pheniramine) in anaphylaxis?

Avil (Pheniramine) Has No Role in Anaphylaxis Treatment

Pheniramine (Avil) should NOT be used in anaphylaxis—epinephrine is the only first-line treatment and must be administered immediately. Antihistamines like pheniramine are adjunctive therapy only for cutaneous symptoms and should never be given before or instead of epinephrine. 1

Why Antihistamines Are Not Appropriate First-Line Treatment

Antihistamines do not address the life-threatening manifestations of anaphylaxis:

• Antihistamines cannot relieve or prevent airway obstruction, hypotension, or shock—the primary causes of death in anaphylaxis 2
• They have a delayed onset of action, reaching maximal plasma concentrations in 1-3 hours compared to <10 minutes for intramuscular epinephrine 2
• Histamine is only one of multiple mediators released during anaphylaxis; blocking histamine receptors alone is insufficient 1, 2

Correct First-Line Treatment: Epinephrine

Administer epinephrine immediately upon recognition of anaphylaxis:

• Dose: 0.01 mg/kg of 1:1000 (1 mg/mL) solution intramuscularly, up to maximum 0.5 mg in adults and 0.3 mg in children 1, 3
• Route: Intramuscular injection into the anterolateral thigh (vastus lateralis) 1, 3
• Repeat dosing: Every 5-15 minutes if symptoms persist 1, 3
• No absolute contraindications to epinephrine use in anaphylaxis 1

When Antihistamines May Be Used (As Adjunctive Therapy Only)

After epinephrine administration, antihistamines may help with cutaneous symptoms:

• H1-antihistamines: Diphenhydramine 25-50 mg IV/IM (1-2 mg/kg in children) for urticaria and pruritus 3, 4
• H2-antihistamines: Ranitidine 50 mg IV for adults (1 mg/kg for children) may be considered 3, 4
• These should only be given after epinephrine and do not replace it 1, 5

Critical Pitfalls to Avoid

Common errors that endanger patients:

• Never delay epinephrine to administer antihistamines—delayed epinephrine is associated with fatalities 5, 2
• Never substitute antihistamines or bronchodilators for epinephrine 5, 6
• Antihistamines do not prevent biphasic reactions despite common misconceptions 6
• Chlorpheniramine (a related antihistamine) can itself rarely cause anaphylaxis 7

Complete Anaphylaxis Management Algorithm

After epinephrine administration:

1. Position patient supine with legs elevated (unless respiratory distress present) 3, 5
2. Administer IV fluids: 500-1000 mL crystalloid bolus for adults, 20 mL/kg for children 3
3. Provide supplemental oxygen and monitor vital signs continuously 3, 5
4. For persistent bronchospasm: Albuterol nebulization 2.5-5 mg after epinephrine 3
5. For refractory hypotension: Consider epinephrine infusion 5-15 μg/min 3
6. Observe minimum 6 hours for potential biphasic reactions 3, 5, 4

Second-line adjunctive medications (after epinephrine):

• Corticosteroids: Methylprednisolone 1-2 mg/kg IV or prednisone 0.5 mg/kg orally to potentially prevent biphasic reactions 3
• These provide no acute benefit and should not delay epinephrine 1