Chlorpheniramine Maleate Dosing in Children
Oral Dosing (Standard Use)
For oral administration in children, chlorpheniramine maleate should be dosed at 0.35 mg/kg/day divided every 4-6 hours, with age-based maximum limits: children 6-12 years receive 2 mg every 4-6 hours (maximum 12 mg/24 hours), and children ≥12 years receive 4 mg every 4-6 hours (maximum 24 mg/24 hours). 1
Age-Based Oral Dosing Algorithm:
- Children ≥12 years: 4 mg (one tablet) every 4-6 hours, not exceeding 6 tablets (24 mg) in 24 hours 1
- Children 6 to <12 years: 2 mg (half tablet) every 4-6 hours, not exceeding 3 tablets (12 mg) in 24 hours 1
- Children <6 years: Not recommended for over-the-counter oral use 1
Pharmacokinetic Considerations:
The oral dosing achieves therapeutic serum concentrations of 2.3-12.1 ng/mL for symptom control in allergic rhinitis 2. Peak plasma levels occur at 2-4 hours after oral administration, with a mean half-life of 13.1 hours in children 2. The elimination half-life in children (mean 9.6 hours) is shorter than in adults due to higher clearance rates (234-470 mL/hr/kg) 3.
Injectable Dosing (Anaphylaxis/Emergency Use)
For anaphylactic reactions, injectable chlorpheniramine maleate must be administered as a slow IV or IM injection using strict age-based dosing: 10 mg for children >12 years, 5 mg for ages 6-12 years, 2.5 mg for ages 6 months to 6 years, and 250 mcg/kg for infants <6 months. 4
Age-Based Injectable Dosing Algorithm:
- Children >12 years: 10 mg IM or slow IV 4
- Children 6-12 years: 5 mg IM or slow IV 4
- Children 6 months to 6 years: 2.5 mg IM or slow IV 4
- Infants <6 months: 250 mcg/kg (0.25 mg/kg) IM or slow IV 4
Critical Safety Considerations for Injectable Use:
IV administration must always be performed as a slow infusion—never as a rapid bolus—to prevent cardiovascular adverse events. 4 This is the most important safety consideration when using injectable chlorpheniramine.
Injectable chlorpheniramine is specifically indicated as an adjunct to epinephrine and hydrocortisone in anaphylactic reactions occurring during anesthesia 4. The drug should not be confused with pheniramine maleate, which has different dosing recommendations 4.
Common Pitfalls and Caveats:
Accumulation Risk with Frequent Dosing:
The long elimination half-life (13-28 hours) means that dosing every 4-6 hours leads to significant drug accumulation, with accumulation ratios ranging from 4.1 to 9.4 (mean 6.5) 5. This necessitates careful monitoring when using frequent daily dosing regimens, particularly in younger children who may experience more sedation 6.
Age-Related Pharmacokinetic Differences:
Younger children (ages 2-5 years) experience more sedation as the most common adverse effect 6. However, when using age/weight-based dosing nomograms, similar maximum concentrations (Cmax) and area under the curve (AUC) are achieved across age groups 6. Clearance and volume of distribution increase with age, but after allometric scaling, no age-related differences exist 6.
Tissue Binding:
The large volume of distribution (7.0 L/kg in children, range 1.20-5.46 L/kg) indicates extensive tissue binding, which is an important aspect of chlorpheniramine pharmacokinetics 2, 3. This explains why therapeutic effects persist even when serum levels decline.