Pheniramine Maleate (Avil) IM vs IV Dosing
The intramuscular and intravenous doses of pheniramine maleate (Avil) are the same at 30.5 mg for adults, as both routes achieve comparable therapeutic plasma concentrations and clinical effects. 1
Evidence-Based Dosing
The pharmacokinetic study directly comparing IV and oral administration of pheniramine demonstrates that:
- Standard adult dose: 30.5 mg (free base equivalent) for both IM and IV routes 1
- After IV administration, peak serum concentrations ranged from 231-894 ng/ml 1
- After oral administration, peak concentrations of 173-274 ng/ml were achieved in 1-2.5 hours 1
- Area under the curve (AUC) values were similar: 3035-4662 ng/ml×h (IV) versus 3507-5768 ng/ml×h (oral), indicating comparable bioavailability 1
Pharmacokinetic Considerations
Terminal half-life is prolonged regardless of route:
This extended half-life has important clinical implications for dosing frequency and potential accumulation with repeated administration.
Route Selection Guidelines
Choose IV route when:
- Immediate onset is required for severe allergic reactions 1
- Patient cannot tolerate oral medications 1
- Rapid achievement of peak plasma levels is necessary 1
IM administration is acceptable when:
- IV access is unavailable or difficult 1
- Slightly delayed onset (similar to oral) is clinically acceptable 1
Critical Safety Warnings
Overdose risk is significant with both routes:
- Doses exceeding therapeutic range (e.g., 50 tablets consumed) can cause life-threatening toxicity including ventricular tachycardia, rhabdomyolysis with myoglobinuria, acute kidney injury, and seizures 2
- Antimuscarinic effects include mucosal dryness, vision changes, hallucinations, and CNS excitation 2
- Cardiotoxicity, though rare, has been documented 2
Monitor for accumulation with repeated dosing: