Recommended Dose of Avil (Pheniramine) for Acute Drug Reactions
For acute drug reactions including hypersensitivity reactions and dystonic reactions, administer pheniramine (Avil) at 1-2 mg/kg IV or IM, with a maximum initial dose of 50 mg. 1
Dosing Protocol
Adult Dosing
- IV/IM route: 1-2 mg/kg per dose 1
- Maximum initial dose: 50 mg 1
- Oral route (when appropriate): 4-12 mg as a single nocturnal dose for ongoing allergic conditions 2
Pediatric Dosing
The dosing varies significantly by age group:
Administration Considerations
Route Selection
- IV administration should be given slowly over 2-3 minutes to avoid pain at the injection site and reduce risk of seizures 1
- IM route is acceptable when IV access is not immediately available 1
- Rapid IV administration may precipitate seizures, so controlled infusion is critical 1
Role in Acute Reactions
Pheniramine serves as an adjunctive medication alongside epinephrine and hydrocortisone in managing anaphylactic reactions, not as primary therapy 2. It is indicated for acute hypersensitivity reactions and dystonic reactions as part of a comprehensive treatment approach 1.
Important Safety Considerations
Common Adverse Effects
- Sedation is the most common side effect and should be anticipated 1, 2
- Respiratory suppression may occur, particularly when combined with other sedative agents 1
- Paradoxical excitement or agitation can develop, especially in younger children 1
- Hypotension may occur, particularly with rapid administration 1
Contraindications and Precautions
- Avoid in severe hepatic disease as sedative effects may precipitate hepatic coma 2
- Contraindicated in angle-closure glaucoma, prostatic hypertrophy, and urinary retention 2, 3
- Avoid concomitant use with MAOIs and medications with anticholinergic effects 2, 3
- Consider dose reduction in moderate renal insufficiency (creatinine clearance 10-20 mL/min) 2, 3
Special Populations
- Pregnancy: Should be avoided, especially during the first trimester, despite a long safety history 2, 3
- Elderly patients: Start with lower doses due to increased sensitivity to anticholinergic effects 3
- Lactation: Should be avoided 2
Clinical Pitfalls to Avoid
Monitoring Requirements
- Monitor vital signs and oxygen saturation during and after administration 1
- Be prepared to provide respiratory support, as there is increased risk of apnea when pheniramine is combined with other sedative agents 1
- Watch for paradoxical agitation, particularly in pediatric patients 1
Drug Interactions
The anticholinergic effects are particularly problematic in elderly patients and those with severe hepatic disease 2. Avoid combining with other anticholinergic medications or MAOIs to prevent additive toxicity 2, 3.
Overdose Considerations
Pheniramine overdose can cause serious toxicity including antimuscarinic effects (dry mucous membranes, blurred vision, hallucinations), CNS excitation (irritability, insomnia, seizures), rhabdomyolysis, myoglobinuria, acute kidney injury, and rarely cardiotoxicity including ventricular tachycardia 4. Aggressive supportive therapy is essential in overdose situations 4.