What is the recommended dosage of chlorpheniramine (antihistamine) for pediatric (paeds) patients?

Chlorpheniramine Pediatric Dosing

For anaphylaxis or acute allergic reactions, chlorpheniramine should be dosed at 250 µg/kg (0.25 mg/kg) for infants under 6 months, 2.5 mg for children 6 months to 6 years, 5 mg for children 6-12 years, and 10 mg for those over 12 years, administered IM or IV slowly. 1

Emergency/Acute Allergic Reaction Dosing

The most authoritative dosing comes from the Association of Anaesthetists' anaphylaxis guidelines, which provides clear age-stratified dosing for acute situations 1:

• < 6 months: 250 µg/kg (0.25 mg/kg) 1
• 6 months to 6 years: 2.5 mg 1
• 6 to 12 years: 5 mg 1
• > 12 years: 10 mg 1

These doses are administered intramuscularly or intravenously (slowly) in the context of anaphylaxis or severe allergic reactions 1. This represents the highest quality guideline evidence for emergency chlorpheniramine dosing in children.

Oral Dosing for Non-Emergency Use

For routine oral administration (allergic rhinitis, urticaria), FDA labeling provides the following 2:

• 6 to under 12 years: 1/2 tablet (2 mg if using 4 mg tablets) every 4-6 hours, not exceeding 3 tablets (12 mg) in 24 hours 2
• 12 years and over: 1 tablet (4 mg) every 4-6 hours, not exceeding 6 tablets (24 mg) in 24 hours 2
• Under 6 years: Do not use (per FDA labeling) 2

Important Clinical Considerations

Sedation is the most common adverse effect and appears more prevalent in younger children (2-5 years old). 3 Monitor carefully for excessive drowsiness, particularly in this age group.

Pharmacokinetic Considerations

• The half-life of chlorpheniramine in children is approximately 13-15 hours 3, 4
• Therapeutic serum concentrations range from 2.3 to 12.1 ng/ml for symptom control 4
• Age/weight-based dosing achieves similar drug exposure across pediatric age groups when appropriately scaled 3

Critical Safety Warnings

Higher doses of chlorpheniramine have been associated with increased drowsiness and decreased respiratory rates without additional therapeutic benefit. 5 In one study, children receiving 50% higher doses experienced significantly lower respiratory rates on multiple assessment days and higher rates of drowsiness (86.3% vs 66.7%) 5.

Avoid using chlorpheniramine in children under 6 months except in emergency situations (anaphylaxis) where the weight-based dose of 250 µg/kg should be used. 1, 2

Route-Specific Guidance

For parenteral administration in acute settings:

• Administer IM or IV slowly to minimize adverse effects 1
• IV administration should be given slowly to avoid potential complications 1
• In anaphylaxis, chlorpheniramine is adjunctive therapy—epinephrine remains the primary treatment 1

Common Pitfalls to Avoid

• Do not exceed maximum daily doses: Overdosing increases sedation and respiratory depression risk without improving efficacy 5
• Do not use oral formulations in children under 6 years outside of emergency protocols 2
• Do not confuse chlorpheniramine with diphenhydramine dosing: These are different medications with different dosing schedules 1
• Monitor respiratory rate closely when using higher doses or in younger children 5