Paediatric Dosing: How mg/kg Works in Children
A reference explanation of paediatric weight-based dosing — why children are not small adults pharmacologically, how developmental changes alter drug handling, and why paediatric dose errors are so consequential.
This is an explanatory reference, not a dosing calculator. Paediatric doses should come from the product label, a prescriber, or a pharmacist — never from an online calculator. If you are trying to work out how much medicine to give a child right now, read the label on the package or call your pharmacist. If you think a child has taken too much, contact poison control or emergency services immediately.
Formula & Reference
| Variable | Symbol | Formula | Units |
|---|---|---|---|
| Paediatric Dosing: How mg/kg Works in Children | — | Concept reference — no dose output | concept |
Step-by-Step Examples
Paediatric dosing is not adult dosing scaled down proportionally.
- Neonates have immature hepatic enzyme systems and reduced renal clearance
- Infants have a higher proportion of body water, altering distribution
- Toddlers and young children often clear some drugs faster per kilogram than adults
- Adolescents approach but do not always reach adult handling
- Each stage requires its own reference, not interpolation
The same absolute error means far more in a small child.
- A tenfold decimal error in a 5 kg infant can be immediately life-threatening
- Paediatric formulations come in multiple concentrations, inviting confusion
- Volume measurement of small doses is intrinsically less precise
- Children have less physiological reserve to tolerate an overdose
Parents searching for a children's dose are the population this page is most concerned about.
- Over-the-counter paediatric products already carry weight and age-banded dosing on the label
- Many liquid preparations exist at different concentrations for the same drug
- Combination products can duplicate an ingredient without it being obvious
- Recent doses given by another caregiver may not be known
Real-World Applications
Common Mistakes to Avoid
Drug clearance per kilogram varies non-linearly with age. Neonates often need less per kilogram than toddlers, who may need more per kilogram than adults for the same drug.
The same drug may be sold at several strengths. Measuring the right volume of the wrong concentration is a recognized cause of serious paediatric overdose.
Household teaspoons vary widely in actual volume. Only the supplied oral syringe or dosing cup should be used.