The right dose, the right cap, the right child — analgesic and antipyretic prescribing

Candidate brief

You are the paediatric registrar on the ward overnight. A six-year-old boy, 21 kg, has just been admitted after reduction and backslabbing of a displaced both-bone forearm fracture. He is tearful and guarding the arm, drinking small sips of water, and has a fever of 38.8 °C with a coryzal viral illness. The ward nurse asks you to confirm the analgesic and antipyretic plan and to calculate the doses. A medical student suggests alternating paracetamol and ibuprofen every two hours and offers aspirin for the fever. [2]

You have ten minutes to: confirm the weight and score the pain; choose and calculate the analgesic and antipyretic doses with the adult ceiling; take a position on the alternating suggestion and the aspirin offer; plan the opioid escalation and its monitoring if simple analgesia is inadequate; and prepare the discharge communication and safety-net. [2]

The encounter

1. Confirm the foundation

The candidate confirms a measured weight of 21 kg on a calibrated scale, scored in kilograms. The pain is scored with a 0-to-10 numerical rating scale (or faces scale) and is moderate; the child is alert, drinking and passing urine, so an NSAID is not contraindicated on hydration grounds. The candidate asks what the family has already given, because the commonest paracetamol ceiling breach is a second preparation. [2]

2. Calculate and prescribe

The candidate prescribes paracetamol 15 mg per kg per dose — 315 mg per dose (rounded to an available formulation), every four to six hours, maximum 60 mg per kg per day (1.26 g per day, well below the 4 g per day adult cap, checked explicitly). The candidate adds ibuprofen 5 to 10 mg per kg per dose — roughly 100 to 200 mg per dose, every six to eight hours, maximum 30 mg per kg per day, from three months and over 5 kg — and notes that the child is drinking and passing urine, with no renal impairment, bleeding risk or aspirin-sensitive asthma, so the NSAID is appropriate given the inflammatory component of the fracture. [2] [3]

3. The alternating and aspirin questions

The candidate declines routine alternating: the 2024 network meta-analysis supports a modest short-term advantage for dual therapy but an increased risk of dosing error, so the position is a single effective agent with a clear plan, with dual therapy here justified by combined pain and fever but given on a written schedule with a stated maximum daily dose and a dosing syringe — not as an every-two-hour alternation. The candidate declines the aspirin offer outright: aspirin is avoided in children under 16 with viral illness because of Reye syndrome; paracetamol or ibuprofen is the correct antipyretic. [1] [6]

4. Plan the opioid escalation

The candidate states that if the pain is not controlled with regular paracetamol and ibuprofen, the next step is a low-dose opioid — morphine 0.1 to 0.2 mg per kg intravenously, titrated to the pain score and monitored with a sedation score, respiratory rate and continuous observation in the first hours. The candidate names codeine and tramadol as contraindicated in children under 12 (and after tonsillectomy) because a CYP2D6 ultrarapid metaboliser converts the prodrug to a fatal morphine overdose, and so neither is an option for this six-year-old. The candidate names the response to opioid respiratory depression: naloxone titrated to the respiratory rate, with monitoring for recurrence. [7] [12]

5. Document and safety-net

The candidate writes the dose in milligrams with a leading zero and no trailing zero, double-checks the calculation independently, and at discharge writes the dose in milligrams (not millilitres alone), provides a dosing syringe, states the maximum daily dose, and teaches back to the family. The written safety-net names reduced feeding, reduced wet nappies, lethargy or drowsiness, a fever that does not settle, increasing pain despite analgesia, and any non-blanching rash as features that should bring the child back urgently. Fracture clinic follow-up is arranged. [2] [11]

Marking domains