How should pediatric medication doses be calculated safely using weight‑based (mg/kg) guidelines, maximum single‑dose and daily limits, and appropriate formulations?

Pediatric Medication Dosing: Weight-Based Calculation and Safety Framework

Calculate all pediatric medication doses using weight-based (mg/kg) guidelines, never scale down from adult doses, and always verify that the calculated dose does not exceed the maximum single-dose or daily limits specified for each medication. 1, 2

Core Dosing Principles

Weight-Based Calculation is Mandatory

• Use mg/kg dosing for all pediatric medications as the primary calculation method, accounting for age-specific pharmacokinetic differences in absorption, distribution, metabolism, and elimination. 1, 2
• Children are not small adults—simple proportional scaling from adult doses is inappropriate and dangerous, as it systematically underdoses older children and overdoses neonates. 3, 2
• For infants under 3 months, organ immaturity (particularly renal function and glucuronidation pathways) requires specific age-adjusted dosing that differs from older children. 1, 4

Maximum Dose Limits Are Absolute

• Always apply the maximum single-dose and maximum daily dose caps even when weight-based calculations exceed these limits. 5, 1
• For example, isoniazid in children is dosed at 10-15 mg/kg daily but never exceeds 300 mg maximum, regardless of weight. 5, 3
• Rifampin follows 10-20 mg/kg dosing with a 600 mg maximum daily dose. 5, 3

Age-Specific Dosing Adjustments

Neonates and Infants Under 3 Months

• Limit amoxicillin to 30 mg/kg/day divided every 12 hours due to incompletely developed renal function affecting drug elimination. 4
• Acetaminophen dosing is 15 mg/kg per dose for infants weighing less than 10 kg. 1
• Oseltamivir requires precise age-based adjustments: 3 mg/kg/dose twice daily for term infants 0-8 months, and 3.5 mg/kg/dose twice daily for infants 9-11 months. 6, 1

Children 3 Months and Older

• Standard weight-based dosing applies, with formulations selected based on ability to swallow tablets versus need for liquid suspensions. 4
• For mild-to-moderate infections, amoxicillin is dosed at 25 mg/kg/day divided every 12 hours or 20 mg/kg/day divided every 8 hours. 4
• For severe infections, increase to 45 mg/kg/day divided every 12 hours or 40 mg/kg/day divided every 8 hours. 4

Dose Rounding and Measurement Safety

Therapeutic Index Determines Rounding Tolerance

• Narrow therapeutic index drugs (e.g., digoxin, warfarin, chemotherapy) must be rounded only to the nearest 0.1 mL or not rounded at all to prevent toxicity. 6, 1
• Standard medications with wider therapeutic windows can tolerate rounding up to 10% after expert consensus (e.g., metoclopramide). 6, 1
• Dose-dependent toxicity drugs should be rounded down to easily administered volumes while respecting maximum dose guidelines. 6

Practical Formulation Selection

• Liquid suspensions allow precise weight-based dosing for children unable to swallow tablets. 4
• After reconstitution, oral suspensions must be shaken well before each use and discarded after 14 days. 4
• Administer suspensions directly on the child's tongue or mix with formula, milk, or juice for immediate consumption. 4

Critical Medication-Specific Examples

Emergency Medications

• Epinephrine for anaphylaxis: 0.01 mg/kg (0.01 mL/kg of 1:1000 solution) intramuscularly, maximum 0.3 mg per dose, repeat every 5 minutes as needed. 6, 1
• Lorazepam for seizures: 0.05-0.15 mg/kg IV/IM, maximum single dose 5 mg. 1
• Glucose for hypoglycemia: 0.5-1.0 g/kg as D10W (2-4 mL/kg of D25W or 1-2 mL/kg of D50W). 1

Common Antibiotics

• Amoxicillin-clavulanate: 20-40 mg/kg/day (amoxicillin component) divided into 3 doses, maximum 4000 mg amoxicillin daily. 3
• Cephalexin for UTI: 50-100 mg/kg/day divided into 4 doses. 3
• Vancomycin for MRSA: 40-60 mg/kg/day divided every 6-8 hours. 1, 3

Antituberculosis Medications

• Isoniazid: 10-15 mg/kg daily (maximum 300 mg) for children. 5, 3
• Rifampin: 10-20 mg/kg daily (maximum 600 mg) for children. 5, 3
• Pyrazinamide: 15-30 mg/kg daily (maximum 2.0 g) for children. 5
• Ethambutol: 15-20 mg/kg daily (maximum 1.0 g) for children. 5

Renal Impairment Adjustments

Dose Reduction Requirements

• Patients with glomerular filtration rate (GFR) less than 30 mL/min should NOT receive the 875 mg amoxicillin dose formulation. 4
• For GFR 10-30 mL/min: reduce to 500 mg or 250 mg every 12 hours depending on infection severity. 4
• For GFR less than 10 mL/min: reduce to 500 mg or 250 mg every 24 hours. 4
• Hemodialysis patients require an additional dose both during and at the end of dialysis. 4
• Renally eliminated drugs (aminoglycosides, beta-lactams) require dose adjustment in all degrees of renal impairment. 3

Treatment Duration and Monitoring

Standard Treatment Courses

• Most infections require continuation for 48-72 hours beyond symptom resolution or bacterial eradication. 5, 4
• Streptococcus pyogenes infections require at least 10 days of treatment to prevent acute rheumatic fever. 5, 4
• Community-acquired pneumonia typically requires 10-day courses, though shorter courses may be effective for mild outpatient disease. 5
• CA-MRSA infections may require longer treatment than S. pneumoniae infections. 5

Clinical Response Assessment

• Children on adequate therapy should demonstrate clinical and laboratory improvement within 48-72 hours. 5
• Patients who deteriorate or show no improvement within this timeframe require further investigation and possible treatment modification. 5

Critical Pitfalls to Avoid

Drug-Specific Contraindications

• Never use ceftriaxone in hyperbilirubinemic neonates due to bilirubin displacement and kernicterus risk. 3
• Avoid ambrisentan in neonates and infants due to immature glucuronidation pathways. 1
• Rifabutin and rifapentine have unknown or unapproved pediatric dosing and should be avoided when alternatives exist. 5

Calculation Errors

• Verify that age-based dosing recommendations (often found on over-the-counter products) align with weight-based calculations—up to 30% of children receive inadequate doses when age-based dosing is used. 7
• For acetaminophen specifically, 10 mg/kg doses fail to reach therapeutic plasma concentrations (10-20 μg/mL), while 15 mg/kg is the minimum effective dose. 7
• Double-check that calculated doses fall within both the mg/kg range AND do not exceed maximum limits. 5, 1