What medications are dosed higher in children than in adults?

Medications Dosed Higher in Children Than Adults

Several medications require higher weight-based dosing in children compared to adults due to differences in pharmacokinetics, including faster drug clearance and differences in body composition. Based on the available guidelines, the following medications are typically dosed higher in children than in adults:

Vancomycin

Vancomycin is one of the clearest examples where pediatric dosing exceeds adult dosing:

• Children: 40 mg/kg/day IV in 2-3 divided doses 1
• Adults: 30 mg/kg/day IV in 2 divided doses 1

The higher pediatric dose is necessary because children have faster renal clearance of vancomycin compared to adults.

Amoxicillin

• Children: 20-45 mg/kg/day in divided doses every 8-12 hours 2
• Adults: 750-1750 mg/day (typically 250-500 mg three times daily, which is lower on a per kg basis for most adults) 2

For a 70 kg adult, the maximum recommended dose would be approximately 25 mg/kg/day, which is lower than the upper range for children.

Other Antibiotics with Higher Pediatric Dosing

1. Linezolid:

   • Children: 10 mg/kg/dose every 8 hours (30 mg/kg/day) 1
   • Adults: 600 mg every 12 hours (approximately 17 mg/kg/day for a 70 kg adult) 1

2. Rifampin (when used in endocarditis):

   • Children: 20 mg/kg/day in 3 divided doses 1
   • Adults: 900 mg/day in 3 divided doses (approximately 13 mg/kg/day for a 70 kg adult) 1

3. Ceftriaxone:

   • Children: 50-75 mg/kg/day 1
   • Adults: Typically 1-2 g/day (approximately 14-28 mg/kg/day for a 70 kg adult)

Physiological Basis for Higher Pediatric Dosing

The need for higher weight-based dosing in children is primarily due to:

1. Faster drug clearance: Children generally have higher metabolic rates and faster renal clearance per kg of body weight 3

2. Different body composition: Children have a higher percentage of water and lower percentage of fat compared to adults, affecting drug distribution 4

3. Developmental differences in drug metabolism: Children's enzyme systems may metabolize certain drugs more rapidly than adults 3

Important Considerations

• Weight-based dosing cannot simply be scaled down from adults to children, as this often results in underdosing in children 4

• Children aged 2 years and older are pharmacokinetically similar to adults in terms of maturation but differ in size, while neonates and infants have immature elimination pathways 4

• For obese children, dosing may need to be based on ideal body weight or adjusted body weight rather than total body weight for certain medications 5

Clinical Implications

Understanding these dosing differences is crucial for safe and effective medication administration in pediatric patients. Using adult dosing parameters for children can result in treatment failure due to subtherapeutic drug levels.

The 2014 FDA study demonstrated that pediatric dosing should not be determined by simply applying weight-based calculations to adult doses, as drug clearance is highly variable in the pediatric population and not readily predictable based on adult information 3.