Pediatric Dosing for Ibuprofen (Motrin) and Acetaminophen (Tylenol) for a 105-pound Patient
For a 105-pound (48 kg) patient, administer ibuprofen 10 mg/kg (480 mg) every 6-8 hours and acetaminophen 15 mg/kg (720 mg) every 4-6 hours, using weight-based dosing rather than age-based recommendations.
Weight-Based Dosing Calculations
Ibuprofen (Motrin)
- Weight: 105 lbs = 47.7 kg (round to 48 kg)
- Dose: 10 mg/kg = 480 mg per dose
- Frequency: Every 6-8 hours
- Maximum daily dose: Do not exceed 2400 mg/day (adult maximum)
Volume in mL:
- If using children's suspension (100 mg/5 mL): 24 mL per dose
- If using infant drops (50 mg/1.25 mL): Not recommended for this weight—use children's suspension
Since this patient weighs >40 kg, they qualify for adult dosing per FDA labeling 1. The adult dose is 200-400 mg every 4-6 hours, but weight-based dosing of 10 mg/kg (480 mg) is more appropriate and supported by clinical evidence 2, 3.
Acetaminophen (Tylenol)
- Weight: 48 kg
- Dose: 15 mg/kg = 720 mg per dose
- Frequency: Every 4-6 hours
- Maximum daily dose: Do not exceed 4000 mg/day (adult maximum)
Volume in mL:
- If using children's suspension (160 mg/5 mL): 22.5 mL per dose
- If using infant drops (80 mg/0.8 mL): Not recommended for this weight—use children's suspension
For patients ≥12 years or >40 kg, adult dosing applies per FDA labeling 4, but weight-based dosing of 15 mg/kg provides more precise analgesia and antipyresis 2.
Key Clinical Considerations
Use weight-based dosing, not age-based dosing, for all pediatric patients. Children weighing >40 kg should receive weight-based calculations rather than defaulting to standard adult doses, as this optimizes efficacy while maintaining safety 5, 6, 5.
Ibuprofen at 10 mg/kg is more effective than lower doses (5 mg/kg) for fever reduction at 2,4, and 6 hours post-administration 2, 3. The 10 mg/kg dose demonstrates equivalent efficacy to acetaminophen 15 mg/kg for pain relief but superior antipyretic effects 2.
Avoid using infant concentration products for larger children. Research demonstrates significantly higher dosing errors with infant ibuprofen (200 mg/5 mL) compared to children's formulation (100 mg/5 mL), with mean absolute errors of 39 mg vs 27 mg respectively 7. For a 48-kg patient, use children's suspension exclusively.
Practical Dosing Instructions
For Ibuprofen:
- Measure 24 mL of children's ibuprofen suspension (100 mg/5 mL)
- Administer every 6-8 hours as needed
- Do not exceed 4 doses in 24 hours
For Acetaminophen:
- Measure 22.5 mL of children's acetaminophen suspension (160 mg/5 mL)
- Administer every 4-6 hours as needed
- Do not exceed 5 doses in 24 hours
Use an oral syringe for accurate measurement rather than dosing cups, which are associated with higher error rates 7.
Combination or Alternating Therapy
If monotherapy provides inadequate relief, combined or alternating therapy may be superior to single-agent treatment 8. Combined therapy (both drugs given simultaneously) and alternating therapy (drugs given at staggered intervals) both demonstrate better fever reduction at 4 and 6 hours compared to acetaminophen alone 8. However, this approach increases complexity and risk of dosing errors—reserve for cases where single-agent therapy fails.
Safety Profile
Both medications demonstrate similar safety profiles at recommended doses 2. No significant differences in adverse events occur between ibuprofen 10 mg/kg and acetaminophen 15 mg/kg 9, 2, 3. Monitor for hypothermia with acetaminophen (rare but reported) and gastrointestinal symptoms with ibuprofen 3.