What is the appropriate intravenous dose of pheniramine maleate (Avil) for adults and children, including weight‑based dosing for younger children?

Intravenous Dose of Pheniramine (Avil)

For adults and children, administer pheniramine maleate at 1-2 mg/kg IV per dose, with a maximum initial dose of 50 mg, diluted in 10 mL of 0.9% sodium chloride or 5% dextrose and given slowly over 2-5 minutes. 1, 2

Dosing Algorithm

Adult Dosing

• Standard dose: 1-2 mg/kg IV per dose 1, 2
• Maximum initial dose: 50 mg regardless of weight 1, 2
• Route: IV or IM (IM acceptable when IV access unavailable) 1

Pediatric Dosing

• Standard dose: 1-2 mg/kg IV per dose 1, 2
• Maximum initial dose: 50 mg regardless of weight 1, 2
• Younger children/infants: Use lower end of dosing range (1 mg/kg) 1
• Older children/adolescents: Full 1-2 mg/kg dose can be used, not exceeding 50 mg maximum 1

Critical Administration Requirements

Preparation and Dilution

• Must dilute in at least 10 mL of compatible solution (0.9% sodium chloride or 5% dextrose) 2
• Never administer undiluted IV push 2

Infusion Rate

• Administer slowly over 2-5 minutes minimum 1, 2
• Rapid administration significantly increases seizure risk 1, 2

Role in Clinical Context

Anaphylaxis Management

• Pheniramine is NEVER first-line therapy for anaphylaxis 1, 2
• Epinephrine must be given first 1, 2
• Pheniramine serves only as adjunctive second-line therapy after epinephrine and fluid resuscitation 1
• Combination with H2-blockers (such as ranitidine 1 mg/kg) is superior to H1-antihistamine alone 1, 2

Acute Hypersensitivity Reactions

• Standard dose remains 1-2 mg/kg IV/IM (maximum 50 mg) 2
• Use as adjunctive medication alongside epinephrine and hydrocortisone, not as primary therapy 1

Critical Safety Warnings

Life-Threatening Risks with Rapid Administration

• Seizures (most critical concern with rapid IV push) 1, 2
• Hypotension 1, 2
• Respiratory suppression and apnea 1, 2
• Paradoxical excitement or agitation (especially in younger children) 1, 2

Monitoring Requirements

• Monitor vital signs and oxygen saturation continuously during and after administration 1
• Be prepared to provide respiratory support, as apnea risk increases when combined with other sedative agents 1
• Watch for paradoxical agitation, particularly in pediatric patients 1

Contraindications and Precautions

Absolute Contraindications

• Angle-closure glaucoma 1
• Prostatic hypertrophy 1
• Urinary retention 1
• Severe hepatic disease (sedative effects may precipitate hepatic coma) 1

Drug Interactions to Avoid

• MAOIs (monoamine oxidase inhibitors) 1
• Other anticholinergic medications (additive toxicity risk) 1
• Other sedative agents (increased respiratory suppression risk) 1

Special Populations

Pregnancy and Lactation

• Avoid during pregnancy, especially first trimester 1
• Avoid during lactation 1

Elderly Patients

• Start with lower doses due to increased sensitivity to anticholinergic effects 1

Common Pitfalls to Avoid

1. Never use pheniramine as monotherapy in anaphylaxis - epinephrine must be given first 1, 2
2. Never give undiluted IV push - always dilute in at least 10 mL 2
3. Never administer rapidly - use minimum 2 minutes infusion time 2
4. Do not combine with other anticholinergic medications or MAOIs to prevent additive toxicity 1
5. Monitor for respiratory depression, especially when combined with benzodiazepines or opioids 2

Most Common Side Effect

Sedation is the most common side effect and should be anticipated in all patients 1