Chlorpheniramine Dosing for Intramuscular Administration in Children
For intramuscular administration of chlorpheniramine in children, the recommended dosage is 250 μg/kg (0.25 mg/kg) for infants under 6 months, with age-based fixed dosing for older children. 1
Age-Based Dosing Guidelines
The appropriate intramuscular dose of chlorpheniramine for children varies by age group:
| Age Group | Chlorpheniramine Dosage (IM) |
|---|---|
| > 12 years | 10 mg |
| 6-12 years | 5 mg |
| 6 months-6 years | 2.5 mg |
| < 6 months | 250 μg/kg (0.25 mg/kg) |
Clinical Context and Administration
Chlorpheniramine is commonly used in pediatric emergency settings, particularly for:
- Acute hypersensitivity reactions
- Anaphylaxis (as adjunctive therapy after epinephrine)
- Allergic reactions
Administration Considerations:
- Administer IM injections slowly
- For anaphylaxis, chlorpheniramine should be given as part of secondary management after epinephrine and fluid resuscitation 1
- Monitor for sedation, which is more common in younger children (2-5 years) 2
Pharmacokinetic Considerations
Several important pharmacokinetic factors influence chlorpheniramine dosing in children:
- Children have a shorter elimination half-life (mean 9.6 hours) compared to adults (22-28 hours) 3, 4
- Volume of distribution in children ranges from 1.20 to 5.46 L/kg 3
- Clearance rates in children (234-470 mL/hr/kg) are higher than in adults and generally decrease with age 3
Safety Considerations and Monitoring
Potential Adverse Effects:
- Sedation (most common adverse effect)
- Respiratory depression (especially with higher doses)
- Paradoxical excitement or agitation
- Hypotension with rapid administration
Cautions:
- Avoid rapid IV administration as it may precipitate seizures 1
- Use with caution when combined with other sedative agents
- Higher doses have been associated with increased drowsiness and decreased respiratory rates without additional clinical benefit 5
Clinical Pearls
- Therapeutic serum concentrations range from 2.3 to 12.1 ng/mL for symptom suppression 6
- The large volume of distribution suggests significant tissue binding is important in chlorpheniramine pharmacokinetics 6
- When treating anaphylaxis, always remember that chlorpheniramine is adjunctive therapy - epinephrine remains the first-line treatment 1, 7
- Sedation appears to be more prevalent in younger children (2-5 years) even with weight-adjusted dosing 2
By following these age-based dosing guidelines, clinicians can safely administer intramuscular chlorpheniramine to pediatric patients while minimizing adverse effects and optimizing therapeutic outcomes.