Ibuprofen Dosing for a 12-Year-Old
For a 12-year-old weighing 40-50 kg, administer ibuprofen 400 mg every 4-6 hours as needed for mild to moderate pain or fever, not exceeding 2400 mg per day (maximum 40 mg/kg/day). 1
Weight-Based Dosing Algorithm
- For children weighing ≥40 kg: Use adult dosing of 400 mg every 4-6 hours 1
- For children weighing <40 kg: Calculate 5-10 mg/kg per dose, administered 3-4 times daily 2
- Maximum daily dose: Do not exceed 40 mg/kg/day or 2400 mg/day, whichever is lower 2
The 40 kg threshold is clinically significant because multiple guidelines establish this as the transition point to adult dosing for most medications 3. Since your patient weighs 40-50 kg, adult dosing applies.
Specific Dosing Recommendations
- Single dose: 400 mg is the optimal dose for pain relief 1, 4
- Frequency: Every 4-6 hours as necessary 1
- Duration of action: 6 hours for 400 mg dose (compared to 4-6 hours for 200 mg) 4
- Time to peak effect: Maximum temperature reduction occurs 3-4 hours after administration 5
Clinical trials demonstrate that doses greater than 400 mg provide no additional analgesic benefit in controlled studies 1. The 400 mg dose has been shown superior to paracetamol in sensitive pain models and provides longer duration of action 4.
Administration Considerations
- With food: Administer with meals or milk if gastrointestinal complaints occur 1
- Hydration: Ensure adequate hydration, particularly important in younger patients 2
- Route: Oral route is preferred; rectal administration shows erratic absorption especially in younger patients 2
Safety Profile in This Age Group
Ibuprofen at these doses has an excellent safety profile in adolescents. 6, 5
- Short-term use (days to weeks) at 400 mg doses carries minimal risk of serious adverse events 6
- Better tolerated by children than adults with lower incidence of gastrointestinal, renal, and cardiovascular events compared to other NSAIDs 6, 5
- Safer in overdose than paracetamol or aspirin 5
The pharmacokinetic properties—particularly the short plasma half-life and lack of toxic metabolites—contribute to ibuprofen's favorable safety profile 6.
Common Pitfalls to Avoid
- Do not exceed 2400 mg/day in adolescents for acute pain/fever management 1
- Avoid chronic high-dose use (≥1800-2400 mg/day) without medical supervision, as this is reserved for inflammatory conditions like juvenile arthritis 1
- Do not use rectal formulations as absorption is unreliable in this age group 2
- Ensure adequate hydration before and during treatment to minimize renal risk 2
Clinical Efficacy
The effective dose range for ibuprofen in children is 7.5-10 mg/kg, with 400 mg falling well within this range for a 40-50 kg patient 5. Ibuprofen has been demonstrated to be equally effective or superior to paracetamol as an antipyretic and analgesic with longer duration of action 5, 4.