What is the appropriate medication dose for a 4-year-old child?

Pediatric Dosing for a 4-Year-Old Child

For a 4-year-old child, medication dosing should be calculated using weight-based dosing (mg/kg) rather than age alone, with the typical weight range being 14-20 kg at this age. 1, 2

General Dosing Principles

Children aged 2 years and older are physiologically mature and differ from adults primarily in size, not in drug metabolism. 2 This means:

• Weight-based dosing (mg/kg) is the standard approach for children under 40 kg 3
• For children weighing less than 30 kg, a practical rule is: (weight × 2)% of the adult dose 1
• Individual dose adjustment based on the specific medication's pharmacokinetics is essential 4

Weight-Based Dosing Framework

For a typical 4-year-old (approximately 14-20 kg):

• Most medications require weight-based calculation in mg/kg/dose 5, 2
• The dose should not simply be scaled down from adult doses, as this results in underdosing in children 2
• Maximum doses should not exceed recommended adult doses even when weight-based calculations suggest higher amounts 3

Common Pitfalls to Avoid

Never assume a 4-year-old needs a "small adult dose" without proper weight-based calculation. 2 Key considerations:

• Elimination pathways in children aged 2+ years are mature, so dosing adjustments for maturation are not needed 2
• Organ function (renal, hepatic) should be assessed if there are underlying medical conditions 4
• Dosage forms appropriate for pediatric administration must be available to prevent dosing errors 5

Medication-Specific Examples

For Influenza Treatment (Oseltamivir):

• Children 14-19.9 kg: 45 mg twice daily for 5 days 6
• Children >15-23 kg: 45 mg twice daily 6

For Drug-Resistant TB:

• Isoniazid: 15-20 mg/kg/day (maximum 300 mg) 6
• Pyrazinamide: 30-40 mg/kg/day 6
• Ethambutol: 20-25 mg/kg/day 6

For Opportunistic Infection Prophylaxis:

• TMP-SMZ: 150/750 mg/m²/day in 2 divided doses 6

Clinical Decision Algorithm

1. Obtain accurate current weight in kilograms 3
2. Calculate dose using medication-specific mg/kg recommendations 2
3. Compare calculated dose to maximum adult dose for that indication 3
4. Use the lower of the two values 3
5. Round to available formulation strengths for practical administration 5