Synopsis
Calculate, prescribe, dispense and administer paediatric medicines safely using current weight, age, indication, formulation, organ function, dose ceilings and independent verification.
- Use the current measured weight in kilograms and record date, time and context; kilograms belong visibly on both the observation and prescribing record.
- First-line UK dose reference is the current BNFC monograph for the exact indication, route, age and formulation, supplemented only by clearly governed specialist guidance.
- Write the formula before calculating: dose per administration equals prescribed mg/kg/dose multiplied by weight in kg.
- If guidance gives mg/kg/day, calculate the total daily amount first and then divide by the stated number of doses; never treat it as mg/kg/dose.
- Apply the stated maximum single dose and maximum daily dose after the weight calculation; a larger child must not exceed the ceiling.
- Convert the verified drug dose to volume only after checking the exact concentration: volume in mL equals required mg divided by mg/mL.
- Prescribe both dose and measurable volume for liquids where the system permits, and specify formulation strength because different liquids may contain different mg per mL.
- Use a leading zero for values below one, never a trailing zero, write micrograms in full where ambiguity is possible and avoid unsafe abbreviations.
- Independently check high-risk medicines, neonatal doses, infusions, unusual doses and manual calculations according to local policy; the checker repeats rather than watches the first calculation.
- For childhood obesity, use the drug-specific actual, ideal or adjusted body-weight recommendation; no single size descriptor is safe for all medicines.
- Review kidney and liver function, allergy, interactions, previous doses, cumulative 24-hour exposure and duplicate active ingredients before signing.
- After administration, monitor the intended clinical response and toxicity and reconcile the discharge formulation, device and caregiver teach-back.
Key red flags
A calculated dose above the BNFC age or adult maximum, or outside the local electronic hard limit, must be resolved before administration rather than accepted because the arithmetic is correct.
Confusion between mg and mL, micrograms and milligrams, or mg/kg/dose and mg/kg/day commonly creates tenfold or greater errors.
A weight copied from months earlier, entered in pounds, estimated without necessity or distorted by oedema can make every subsequent calculation unsafe.
Neonates need gestational age, postnatal age and often postmenstrual age because clearance and dose interval change rapidly after birth.
Renal or hepatic impairment, obesity, extracorporeal support and interacting medicines invalidate a simple total-body-weight calculation for many drugs.
Investigation priorities
Provide the denominator for dose and fluid calculations.
Identify the authoritative age, route, indication, interval and maximum.
Management branches
A medicine is prescribed in mg/kg or micrograms/kg.
- Verify patient, current kg weight, indication, route, age band and the current BNFC dose expression.
- Calculate the dose with written units, divide daily doses correctly and apply single and daily maxima.
- Check the actual concentration, calculate mL, round only by the authorised rule and document an independent check when required.