A paracetamol prescription that is dosed by volume, not by weight
A 3-year-old boy weighing 14 kg is brought to the evening OPD at 21:00 with fever of 39.3 degrees Celsius for two days, mild coryza and cough, and one episode of vomiting. He is alert, drinking, has no rash and no neck stiffness, and his mother says he passed urine an hour ago. A private practitioner's prescription reads: Paracetamol 250 mg/5 mL syrup, 5 mL every 4 hours, day and night, until fever settles. The mother has already given four doses since 09:00, the last at 20:00, and the fever has not come down. She asks whether she should give the next dose at midnight, and whether she can add an adult tablet from home because the syrup is nearly finished. The pharmacy has run out of the 125 mg/5 mL strength.
1. Assess the prescription in mg/kg terms, per dose and per day, and say whether it is safe.
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Each 5 mL of a 250 mg/5 mL syrup contains 250 mg, which for a 14 kg child is 250 / 14 = 17.9 mg/kg per dose. The usual therapeutic range is 10-15 mg/kg per dose, so a single dose is above range but not dangerous in itself.
The frequency is the real problem. Every 4 hours, day and night, allows up to six doses in 24 hours, giving 1,500 mg/day or about 107 mg/kg/day. The generally accepted maximum is 75 mg/kg/day (many paediatric protocols use 60 mg/kg/day), so this prescription permits roughly 40-75% more than the ceiling if the mother follows it exactly, and she has already given 1,000 mg - about 71 mg/kg - in twelve hours. That is the pattern that produces cumulative hepatotoxicity: paracetamol overdose is not only a single large ingestion, it is also repeated therapeutic excess, especially in a child who is vomiting, dehydrated or not eating, because glutathione stores fall.
What should have been written: 14 kg x 15 mg/kg = 210 mg per dose, i.e. about 4.2 mL of the 250 mg/5 mL syrup or 8.4 mL of the 125 mg/5 mL syrup, no more than four doses in 24 hours. If an accurate measuring syringe is not available, the prescription should not be dispensed at all.
2. What do you advise about the midnight dose and about the adult tablet, and what would you look for on examination?
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I would not give another dose at midnight. He has had four doses in twelve hours, which is already the maximum for a day, so the next dose should be withheld for at least six to eight hours and the total in the next 24 hours capped at four weight-based doses. Fever control then rests on comfort measures - light clothing, tepid sponging, fluids - and on remembering that the aim of an antipyretic is a comfortable child, not a normal thermometer reading.
The adult tablet must be firmly refused. A standard 500 mg tablet is 36 mg/kg for this child in one go, more than twice a therapeutic dose, and adult combination cold tablets often contain paracetamol plus other ingredients that add risk. I would explain this concretely in mg/kg terms to the mother rather than saying it is 'too strong'.
On examination, since he has already received excess paracetamol, I would look for repeated vomiting, right upper quadrant tenderness, lethargy or irritability, and pale or sweaty appearance, and check hydration and blood glucose. A healthy child with a modest one-day excess usually needs observation, not antidote, but worsening vomiting or drowsiness warrants liver function tests and hospital referral. I would also check whether any cough or cold preparation given at home also contains paracetamol, because double counting is common.
3. Beyond the paracetamol, what decides whether this child can be managed at home?
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The paracetamol question is the easy half; the judgement is whether the child is safe at home at all. The key determinants are feeding and hydration, activity level and interaction, respiratory pattern, and whether the caregiver can observe and return. This child is drinking, has passed urine, is alert and has a normal examination apart from coryza, so outpatient care with clear return advice is reasonable.
I would give specific red flags rather than a vague 'come back if worse': drowsiness or difficult to wake, refusal to drink, reduced urine output, fast or laboured breathing, chest indrawing, a rash that does not fade on pressure, neck stiffness, persistent vomiting, or a fit. A fever that continues beyond three days, or any new focal sign, needs reassessment for a secondary bacterial source.
I would also explain that a two-day viral upper respiratory illness does not need antibiotics, and that the value of antipyretics is comfort rather than preventing harm from the fever itself. Finally, the follow-up plan should be explicit - named facility, named day, and a written dose chart with weight-based millilitres - because the failure in this case was not the drug, it was the prescription written in millilitres by habit.