What is the recommended dose of ibuprofen (nonsteroidal anti-inflammatory drug) or acetaminophen (paracetamol) for a child weighing 90 pounds with fever?

Recommended Antipyretic Dosing for a 90-Pound Child

For a child weighing 90 pounds (approximately 41 kg) with fever, administer ibuprofen 10 mg/kg per dose (410 mg) every 6-8 hours OR acetaminophen 15 mg/kg per dose (615 mg) every 4-6 hours, with ibuprofen being the preferred first-line agent based on its longer duration of action.

Weight-Based Dosing Calculations

90 pounds converts to approximately 41 kg, placing this child in the >40 kg weight category for most pediatric dosing guidelines.

Ibuprofen Dosing

• Recommended dose: 10 mg/kg per dose = 410 mg per dose 1, 2
• Frequency: Every 6-8 hours (maximum 3-4 doses per 24 hours) 1, 3
• Maximum daily dose: 30-40 mg/kg/day = 1,230-1,640 mg/day 1, 3
• Practical administration: Round to 400 mg per dose using standard tablet formulations 4

Acetaminophen (Paracetamol) Dosing

• Recommended dose: 10-15 mg/kg per dose = 410-615 mg per dose 1
• Frequency: Every 4-6 hours (maximum 4 doses per 24 hours) 1
• Maximum daily dose: 60 mg/kg/day = 2,460 mg/day 1
• Practical administration: Round to 500-650 mg per dose using standard tablet formulations 4

Clinical Decision Algorithm

Start with ibuprofen as first-line therapy because it provides longer duration of fever control (6-8 hours vs 4-6 hours) and has been shown to be equally or more effective than acetaminophen in comparative trials 2, 5. The maximum temperature reduction occurs 3-4 hours after ibuprofen administration 2.

When to Consider Combination or Alternating Therapy

If fever persists or breakthrough fever occurs despite single-agent therapy:

• Combined dosing: Administer both medications simultaneously at the start of treatment 5, 6
• Alternating dosing: Give ibuprofen first, then acetaminophen 3 hours later 6
• Both approaches provide an additional 2.5-4.4 hours without fever compared to single agents 5, 6

Critical safety consideration: When using two medications, parents must meticulously record all dose times to avoid exceeding maximum recommended doses, as 8-11% of parents inadvertently exceed dosing limits 5. Parents must also avoid all other products containing acetaminophen, including over-the-counter cold remedies 1.

Evidence Supporting These Recommendations

The American Academy of Pediatrics guidelines establish the standard weight-based dosing of ibuprofen at 10 mg/kg every 8 hours and acetaminophen at 10-15 mg/kg every 6 hours 1. Research demonstrates that 10 mg/kg ibuprofen and 15 mg/kg acetaminophen are equally effective after the initial dose, though ibuprofen maintains effectiveness longer 4.

Combined or alternating therapy provides superior antipyresis at 4-6 hours compared to ibuprofen alone, with nearly all children becoming afebrile versus 50% remaining febrile with ibuprofen monotherapy at 6 hours 6. However, this benefit must be weighed against the 8-11% risk of inadvertently exceeding maximum doses when using two medications 5.

Common Pitfalls to Avoid

• Do not underdose: The effective dose range is 7.5-10 mg/kg for ibuprofen; lower doses (2.5-5 mg/kg) are less effective 2, 4
• Avoid rectal administration: Rectal ibuprofen has erratic absorption, especially in younger children 3
• Ensure adequate hydration: Short-term ibuprofen use is safe when special attention is given to patient hydration 3
• Document all doses: When using combination therapy, provide parents with a dosing chart to prevent accidental overdosing 5