Is a single 400 mg dose of ibuprofen appropriate for a 13‑year‑old child weighing approximately 100 lb (≈45 kg)?

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Ibuprofen 400mg Dosing for a 13-Year-Old Weighing 100 lb

Yes, 400 mg of ibuprofen is appropriate and safe for a 13-year-old weighing 100 lb (approximately 45 kg), as this falls within the recommended weight-based dosing range of 5-10 mg/kg per dose.

Weight-Based Dosing Calculation

  • At 45 kg, the appropriate single dose range is 225-450 mg (5-10 mg/kg), making 400 mg well within therapeutic limits 1, 2
  • The effective dose range demonstrated in clinical trials is 7.5-10 mg/kg, which translates to 337.5-450 mg for this patient 2
  • A 400 mg dose represents approximately 8.9 mg/kg, which is in the middle of the recommended therapeutic range and optimal for pain and fever management 1, 2

Dosing Frequency and Maximum Daily Dose

  • This 400 mg dose can be administered 3-4 times daily if needed 1
  • The maximum total daily dose should not exceed 30-40 mg/kg, which equals 1,350-1,800 mg/day for a 45 kg child 1
  • Maximum temperature reduction occurs 3-4 hours after administration, with ibuprofen having a longer duration of action than acetaminophen 2

Important Safety Considerations

  • Ensure adequate hydration before and during ibuprofen use, as dehydration plays an important role in triggering renal damage 3
  • Do not administer to patients with diarrhea and vomiting (with or without fever) due to increased risk of renal complications 3
  • Contraindicated in patients with wheezing, persistent asthma, or during varicella infection 3
  • Ibuprofen should not be routinely used as an antipyretic except in rare cases; it remains the drug of first choice for inflammatory pain in children 3

Clinical Context

  • Children weighing more than 40 kg may use adult dosing in some contexts, but at 45 kg this patient is just above that threshold and the 400 mg dose appropriately bridges pediatric weight-based and adult dosing 4, 5
  • Ibuprofen is better tolerated by children than adults and is safer in overdose than acetaminophen and aspirin 2
  • Short-term use is considered safe in children older than 3 months with body weight above 5-6 kg when hydration is maintained 1

References

2
Research

A general overview of the use of ibuprofen in paediatrics.

International journal of clinical practice. Supplement, 2003

4
Guideline

Pediatric Medication Dosing Guidelines for Children Under 40 kg

Praxis Medical Insights: Practical Summaries of Clinical Guidelines, 2026

5
Guideline

Dosing Regimen for Pediatric Patients

Praxis Medical Insights: Practical Summaries of Clinical Guidelines, 2026

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Professional Medical Disclaimer

This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.

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