Pediatric Dosing: General Principles
For pediatric patients, weight-based dosing using mg/kg is the standard approach for children <40 kg, while children ≥40 kg should receive weight-based dosing unless the adult dose is exceeded 1.
Core Dosing Framework
The fundamental principle is that simple body weight-based scaling from adult doses inadequately accounts for developmental changes in drug disposition and response 2. Pediatric dosing requires consideration of:
- Age-specific physiologic maturation affecting drug metabolism and clearance
- Body composition changes throughout development
- Organ function maturation particularly hepatic and renal systems
Weight-Based Dosing Strategy
For Children <40 kg:
- Use mg/kg dosing as the primary method 1
- Apply drug-specific maximum daily doses to prevent toxicity
- Consider allometric scaling combined with maturation functions for neonates and infants 2
For Children ≥40 kg:
- Use weight-based dosing unless the recommended adult dose for the specific indication is exceeded 1
- Once adult dose is reached, cap at adult maximum
- This prevents overdosing in larger children while ensuring adequate exposure
Special Considerations for Obesity
For children with obesity, fat-free mass (FFM)-based scaling is preferred over total body weight for many drugs 2, 3. The approach varies by drug lipophilicity:
- Lipophilic drugs: May require total body weight dosing due to increased volume of distribution
- Hydrophilic drugs: Consider FFM or ideal body weight to avoid overdosing 1, 3
- Close therapeutic monitoring is essential as obesity alters pharmacokinetics unpredictably
Practical Dosing Rules
A clinically useful approximation for general dosing 4:
- Up to 30 kg: Child's dose = (weight × 2)% of adult dose
- Over 30 kg: Child's dose = (weight + 30)% of adult dose
This follows body surface area curves more closely than simple mg/kg calculations.
Critical Pitfalls to Avoid
Never simply reduce adult doses proportionally - this ignores developmental pharmacology 5, 6. Key errors include:
- Failing to account for immature hepatic/renal function in neonates
- Using total body weight in obese children for hydrophilic drugs
- Exceeding adult maximum doses in large adolescents
- Ignoring drug-specific therapeutic windows and toxicity profiles
Drug-Specific Adjustments
Certain medication classes require particular attention:
- Narrow therapeutic index drugs: Require therapeutic drug monitoring regardless of calculation method 2
- Renally cleared drugs: Adjust for developmental changes in glomerular filtration rate
- Hepatically metabolized drugs: Consider CYP enzyme maturation, particularly in infants <6 months
The absence of pediatric dosing guidelines for many medications increases potential for serious dosing errors 6, making consultation with pediatric pharmacists or specialists advisable for unfamiliar medications.