Chlorpheniramine (Piriton) Dosing for 11-Year-Old Child Weighing 52 kg
For an 11-year-old child weighing 52 kg, the appropriate dose of chlorpheniramine (Piriton) is 5 mg given IM or IV slowly, which does NOT follow a per-kilogram calculation but rather an age-based dosing guideline. 1
Age-Based Dosing (Not Weight-Based)
Chlorpheniramine dosing in children is age-stratified rather than weight-based, which is critical to understand for safe prescribing:
- Children 6 to 12 years: 5 mg (IM or IV slowly) 1
- Children > 12 years: 10 mg 1
- Children 6 months to 6 years: 2.5 mg 1
- Infants < 6 months: 250 µg/kg 1
Your 11-year-old patient falls into the 6-12 years category, making the dose 5 mg regardless of the 52 kg weight. 1
Oral Dosing Alternative
If using oral chlorpheniramine rather than parenteral:
- Children 6 years to under 12 years: 2 mg (half of a 4 mg tablet) every 4-6 hours, not exceeding 3 tablets (12 mg) in 24 hours 2
- Children 12 years and over: 4 mg (1 tablet) every 4-6 hours, not exceeding 6 tablets (24 mg) in 24 hours 2
Critical Dosing Pitfall
Do not calculate chlorpheniramine as mg/kg in children. 1 The evidence clearly demonstrates that pediatric antihistamine dosing follows age-based categories established in anaphylaxis guidelines rather than weight-proportional calculations. 1 This age-based approach accounts for developmental pharmacokinetic differences that cannot be captured by simple weight scaling. 3
Pharmacokinetic Considerations
While not affecting your immediate dosing decision, chlorpheniramine in children aged 6-16 years demonstrates:
- Mean elimination half-life of 13.1 hours 4, 5
- Large volume of distribution (7.0 L/kg), indicating significant tissue binding 4
- Therapeutic serum concentrations of 2.3-12.1 ng/ml for symptom control 4
These pharmacokinetic parameters support the age-based rather than weight-based dosing strategy, as drug distribution and elimination in children over 2 years are qualitatively similar to adults, differing primarily in size-related factors already accounted for in the age categories. 3