Amoxicillin Dosing for a 13-Year-Old with Sinus Infection
For a 13-year-old with a sinus infection, prescribe amoxicillin 875 mg twice daily for 10-14 days, using adult dosing rather than pediatric weight-based calculations. 1, 2
Dosing Rationale
At 13 years old, this patient should receive adult fixed-dose regimens rather than pediatric weight-based dosing, as adolescents at this age typically exceed the weight threshold (40 kg) where adult dosing becomes appropriate 1, 3. The standard adult dose is either:
- Amoxicillin 875 mg twice daily (every 12 hours) for 10-14 days 2, 3
- Alternative: Amoxicillin 500 mg three times daily (every 8 hours) for 10-14 days 4, 2
The twice-daily regimen is preferred as it improves compliance and is associated with significantly less diarrhea compared to three-times-daily dosing 3.
Treatment Duration and Monitoring
- Standard duration: 10-14 days 1, 2, 5
- Assess clinical response at 72 hours (3 days) of treatment 1, 2
- If no improvement or worsening occurs at 3-5 days, consider switching to high-dose amoxicillin-clavulanate (Augmentin) 2, 5
- Continue treatment until the patient has been symptom-free for 7 days 2, 5
When to Consider Augmentin Instead
Switch to amoxicillin-clavulanate 875/125 mg twice daily if: 1, 5
- No improvement after 3-5 days of amoxicillin
- Recent antibiotic use within 4-6 weeks
- Moderate-to-severe disease at presentation
- Suspected resistant organisms or high local resistance rates
- Areas with high prevalence of β-lactamase-producing H. influenzae
Critical Distinction: Bacterial vs. Viral Sinusitis
Antibiotics should ONLY be prescribed for bacterial sinusitis, not viral upper respiratory infections. 2 The European Position Paper on Rhinosinusitis demonstrates that antibiotics provide no benefit for post-viral acute rhinosinusitis in either adults or children, with no difference in cure rates at 14 days and increased adverse events 4.
Bacterial sinusitis criteria include:
- Symptoms persisting ≥10 days without improvement
- Severe symptoms (high fever ≥39°C, purulent nasal discharge) for 3-4 consecutive days at illness onset
- "Double worsening" pattern (initial improvement followed by worsening)
Common Pitfalls to Avoid
- Do not use pediatric weight-based dosing formulations in adolescents who can swallow adult tablets—this is unnecessary and more expensive 1
- Do not treat viral sinusitis with antibiotics—this contributes to antibiotic resistance without providing benefit 2, 5
- Do not fail to reassess at 3-5 days—this delays necessary changes in therapy 2
- Do not prescribe incomplete courses—this can lead to incomplete eradication and relapse 2, 5
Evidence Quality Note
The pediatric evidence base shows that in children aged 4-15 years with post-viral acute rhinosinusitis, amoxicillin at 80 mg/kg/day showed early improvement at day 3 but no difference at day 14 compared to placebo 4. However, for true bacterial sinusitis (which represents a minority of cases), antibiotics remain appropriate first-line therapy 1, 2.