Weight-based paracetamol for a 14 kg child
A 3-year-old boy weighing 14.0 kg is brought to a district pharmacy in Ulaanbaatar with fever of 38.9 °C and right ear pain. The prescription reads: 'Paracetamol suspension 120 mg/5 mL - 5 mL three times daily for 3 days.' The pharmacy has only 100 mL bottles and a 5 mL dosing spoon with 1 mL markings; a 1 mL oral syringe with 0.25 mL graduations is also available. The mother says the child received one 500 mg adult paracetamol tablet yesterday evening because the suspension had run out. She asks whether she can quarter the remaining adult tablets to finish the course. The child takes no other medicines, has no known liver disease, and weighs 14 kg. The pharmacy's pediatric reference gives paracetamol 15 mg/kg per dose every 6 hours as needed, with a maximum of 60 mg/kg/day. The prescription was written two days ago and is otherwise complete.
1. Calculate the weight-based paracetamol dose and the volume to measure. Compare this with the prescribed 5 mL three times daily, including the total daily dose in mg/kg/day, and state how many bottles are needed for 3 days at the maximum frequency. Show your working.
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Step 1 - weight-based dose. 15 mg/kg × 14.0 kg = 210 mg per dose. The suspension contains 120 mg/5 mL = 24 mg/mL. Volume = 210 mg ÷ 24 mg/mL = 8.75 mL. With a 0.25 mL oral syringe, measure 8.75 mL exactly; do not round to 5 mL or 10 mL.
Step 2 - compare with the written order. 5 mL contains 120 mg, i.e. 8.6 mg/kg/dose. Three times daily gives 360 mg/day = 25.7 mg/kg/day. This is both an underdose per dose and the wrong interval: the reference allows every 6 hours (up to four doses), not three times daily.
Step 3 - maximum and supply. 60 mg/kg/day × 14 kg = 840 mg/day. Four doses of 210 mg = 840 mg, exactly the maximum, so no fifth dose. At four doses/day the volume is 4 × 8.75 = 35 mL/day; for 3 days, 105 mL. A single 100 mL bottle is 5 mL short, so dispense two bottles or plan for three doses/day only if the prescriber agrees. At the written 5 mL three times daily, 15 mL/day would last 6.6 days, but that regimen is not the correct weight-based one.
Judgement: clarify the order with the prescriber before dispensing. Do not silently change the label; document the calculated dose and the prescriber's authorization. The child's ear pain also needs medical review, because paracetamol treats fever but not otitis media.
2. The mother asks to quarter the 500 mg tablets. Evaluate this request, including the dose that a quarter or half tablet would deliver, and describe what you would recommend, document, and tell her about the adult tablet already given.
Read the worked answer
Dose check. A quarter of a 500 mg tablet is 125 mg (8.9 mg/kg), only 60% of the 210 mg target. A half tablet is 250 mg (17.9 mg/kg), about 19% above the target and above the reference 15 mg/kg. Neither is accurate. The tablet may not be scored, and splitting produces unequal pieces and loss of powder; a quarter can range widely.
The adult tablet already given. 500 mg in a 14 kg child is 35.7 mg/kg in one dose. A single dose is unlikely to cause serious liver injury in a healthy child, but it is more than twice the recommended single dose and must not be repeated. Ask about vomiting, abdominal pain, drowsiness, and jaundice; if she gave more than one tablet or the child is unwell, refer for same-day assessment. Do not induce vomiting.
Recommendation. Use the 120 mg/5 mL suspension with the 1 mL oral syringe, 8.75 mL every 6 hours as needed, maximum four doses/24 h. If suspension is unavailable, do not substitute quartered adult tablets; contact the prescriber for a suitable alternative (different strength, suppository, or a properly compounded preparation). Write the dose in mL and mg on the label, demonstrate measuring, and advise keeping medicines locked away. Document the refusal to endorse tablet splitting, the prescriber contact, and the counseling.