How long after administering paracetamol (acetaminophen) to a child can a drop in body temperature be expected?

How Long After Paracetamol Administration Does a Child's Temperature Drop?

Paracetamol (acetaminophen) typically begins to reduce a child's fever within 30-60 minutes after administration, with maximum temperature reduction occurring within 1-2 hours. The antipyretic effect is most pronounced in the first hour after administration 1.

Timing of Temperature Reduction

• The highest fall in temperature occurs in the first hour after paracetamol administration 2
• In clinical studies, significant temperature reduction is measurable by 60 minutes post-dose 1
• The mean time for temperature to reach normal with standard-dose paracetamol (15 mg/kg) is approximately 97.5 minutes, while high-dose paracetamol (20 mg/kg) reduces this time to about 85 minutes 1

Factors Affecting Temperature Response

• The dosage of paracetamol significantly impacts the speed and magnitude of temperature reduction:
  • Standard dose (15 mg/kg): Slower temperature reduction, with an average decrease of 0.33°C in the first hour 1
  • Higher dose (20 mg/kg): Faster temperature reduction, with an average decrease of 0.46°C in the first hour 1
• The duration of antipyretic effect varies:
  • Standard dose (15 mg/kg): Effect lasts approximately 4-6 hours (next fever spike at ~5 hours) 1
  • Higher dose (20 mg/kg): Effect lasts longer, with next fever spike at ~7 hours 1

Clinical Considerations

• Paracetamol is considered safe and effective as a first-line antipyretic treatment for children 3
• While paracetamol effectively reduces fever, it's important to note that antipyretics do not prevent febrile seizures and should be used primarily for comfort rather than with the sole aim of reducing body temperature 4
• The recommended pediatric dosing varies globally:
  • UK: 10-15 mg/kg every 4-6 hours (maximum 4 doses per day) 3
  • Australia: 15 mg/kg every 4-6 hours (maximum 60 mg/kg/day) 3

Comparative Efficacy

• Paracetamol and ibuprofen have similar efficacy in reducing fever in children, though some studies suggest parents may subjectively rate ibuprofen as more effective 5
• The combination of paracetamol and ibuprofen causes quicker temperature reduction than either medication alone, but this approach should be reserved for situations where rapid fever reduction is clinically indicated 2

Important Caveats

• Fever itself may not require treatment unless it causes discomfort or distress to the child 3, 6
• Hepatotoxicity can occur with paracetamol overdose (>10 times recommended dose for single ingestion, or >140 mg/kg/day for several days) 3
• When treating fever in children with COVID-19, paracetamol is preferred over NSAIDs until more evidence is available 4

Remember that while paracetamol effectively reduces fever within 1-2 hours, the primary goal of treatment should be the child's comfort rather than normalization of temperature alone 4.