Weight-Based Dosing in Overweight Children
For overweight children under 40 kg, use actual body weight for medication dosing; for children 40 kg or greater, use weight-based dosing unless it exceeds the adult dose, at which point cap at the adult maximum. 1
Primary Dosing Algorithm
For Non-Obese and Overweight Children (BMI <95th percentile):
- Use actual body weight for all medication calculations 1
- Actual body weight closely approximates ideal body weight in this population and provides accurate dosing 1
- Never exceed the recommended adult dose regardless of the child's weight 1
For Obese Children (BMI ≥95th percentile):
The approach differs based on weight threshold:
Children <40 kg:
- Use actual body weight for initial dosing of most medications 2, 1
- The American Heart Association provides a Class 1 recommendation to use actual body weight for resuscitation drugs regardless of body habitus 1
- Length-based estimation tapes (Broselow tapes) estimate the 50th percentile weight for length, effectively representing ideal body weight, and are acceptable alternatives when actual weight is unknown 1
Children ≥40 kg:
- Transition to adult dosing protocols 1, 3
- Calculate weight-based dose but cap at adult maximum dose 4
- For children exactly at 40 kg, weight-based pediatric dosing may provide more precision than adult dosing 5
Medication-Specific Considerations
Drugs Requiring Ideal Body Weight (IBW) or Adjusted Body Weight (AdjBW):
Lipophilic medications (distribute into adipose tissue):
- Consider using total body weight, as volume of distribution is increased in obesity 6, 7
- Examples include antineoplastic agents, succinylcholine, and cefazolin 7
Hydrophilic medications (limited adipose distribution):
- May require IBW or AdjBW to avoid toxicity 8, 6
- Examples include vancomycin, aminoglycosides, and anticoagulants (heparin, enoxaparin, warfarin) 7
- For aminoglycosides: initial dosing with adjusted body weight is recommended, though using total body weight with therapeutic drug monitoring is also appropriate 6
Specific medication requiring IBW:
- Tuberculosis medications should use ideal body weight for dose calculations, with children >40 kg dosed as adults 1
Critical Pitfalls to Avoid
- Do not automatically use total body weight for all medications in obese children - this can lead to toxic doses of hydrophilic drugs 4
- Avoid arbitrary dose adjustments or guesswork - use systematic approaches with IBW/AdjBW calculators when indicated 9
- Document the specific weight used (actual vs. ideal vs. adjusted) on all medication prescriptions to enable pharmacist verification 1
- Monitor therapeutic drug levels when available (vancomycin, aminoglycosides) rather than relying solely on weight-based calculations 7
Practical Implementation
For resuscitation medications specifically:
- Use actual body weight for calculating initial drug doses regardless of body habitus 2, 1
- For subsequent doses, expert providers may adjust based on therapeutic effect 2
- Length-based tapes are more accurate than age-based estimates and are reasonable when actual weight is unknown 2
The implementation of electronic health record calculators for IBW and AdjBW, combined with evidence-based dosing charts, significantly improves adherence to appropriate dosing (from 1.2% to 24.2% correct dosing) 8.