What is the dose of Inj Avil (pheniramine)?

Dosage of Injectable Pheniramine (Avil)

For adults, injectable pheniramine (Avil) should be administered at a dose of 25-50 mg intravenously or intramuscularly as an adjunctive treatment for allergic reactions. 1

Dosing Guidelines

Adult Dosing:

• Standard dose: 25-50 mg IV or IM 1
• Maximum single dose: 50 mg 1
• Administration: Can be given slowly via IV or IM route
• For IV administration: May be diluted and injected slowly over 5 minutes 1

Pediatric Dosing:

• 1-2 mg/kg per dose 1
• Maximum dose: 50 mg 1

Clinical Context and Administration

Role in Allergic Reactions

• Pheniramine is an H1 antihistamine useful for relieving itching and urticaria in allergic reactions 1
• Important: H1 antihistamines like pheniramine do NOT relieve stridor, shortness of breath, wheezing, GI symptoms, or shock 1
• Should be considered adjunctive therapy only and should not be substituted for epinephrine in anaphylaxis 1

Administration Considerations

• IV administration: Should be given slowly to avoid adverse effects
• Can be combined with H2 antagonists (like ranitidine) for superior efficacy 1
• When combined with ranitidine: Pheniramine 25-50 mg IV with ranitidine 50 mg (diluted in 5% dextrose to 20 mL) injected over 5 minutes 1

Precautions and Side Effects

Common Side Effects

• Sedation and cognitive impairment (first-generation antihistamine) 1, 2
• Drowsiness (more common than with newer antihistamines) 2
• These effects may contribute to decreased awareness of anaphylaxis symptoms 1

Serious Adverse Effects (with overdose)

• Antimuscarinic effects: dry mouth, blurred vision, hallucinations 3
• CNS excitation: irritability, insomnia, seizures 3
• Rarely: cardiotoxicity, rhabdomyolysis 3

Alternative Considerations

• For less sedation, consider second-generation H1 antihistamines like cetirizine (10 mg) 1, 4
• In anaphylaxis, remember that epinephrine is the first-line treatment, with antihistamines as adjunctive therapy only 1

Clinical Pearls

• Pheniramine has a relatively long half-life (8-19 hours) 5
• First-generation antihistamines like pheniramine can impair discharge planning from emergency settings due to sedative effects 4
• Document administration details including dose, route, and patient response 1
• For allergic conjunctivitis, topical pheniramine has shown efficacy 6

Remember that in anaphylaxis, epinephrine is the first-line treatment, and antihistamines like pheniramine should never delay epinephrine administration or be used as the sole treatment for severe allergic reactions.