Amoxicillin Dosing for a 3-Year-Old with Sinusitis
For a 3-year-old child with uncomplicated acute bacterial sinusitis, amoxicillin should be dosed at 45 mg/kg/day divided into 2 doses for 10-14 days, or 80-90 mg/kg/day divided into 2 doses if the child has risk factors for resistant bacteria. 1, 2
Determining the Appropriate Dose
Standard-Dose Amoxicillin (45 mg/kg/day)
Use this regimen when the child has uncomplicated disease without the following risk factors: 1, 2
- Age younger than 2 years
- Daycare attendance
- Antibiotic use within the past 4-6 weeks
- Moderate to severe illness presentation
- Living in an area with high prevalence (>10%) of penicillin-resistant S. pneumoniae
Dosing: 45 mg/kg/day divided into 2 doses (approximately every 12 hours) 1, 2
High-Dose Amoxicillin (80-90 mg/kg/day)
Use this regimen when any of the above risk factors are present: 1, 2
Dosing: 80-90 mg/kg/day divided into 2 doses (maximum 2 grams per dose) 1, 2
Rationale: High-dose therapy achieves sinus fluid concentrations adequate to overcome resistance in S. pneumoniae (which causes ~30% of pediatric bacterial sinusitis) and provides coverage against β-lactamase-producing H. influenzae and M. catarrhalis 1
Treatment Duration
Standard duration is 10-14 days or until the child has been symptom-free for 7 days 1, 3
- For infections caused by Streptococcus pyogenes, a minimum of 10 days is required to prevent acute rheumatic fever 1, 4
- Treatment should continue for at least 48-72 hours beyond when the child becomes asymptomatic 4
When to Escalate to Amoxicillin-Clavulanate
Switch to high-dose amoxicillin-clavulanate (90 mg/kg/day of amoxicillin component with 6.4 mg/kg/day clavulanate in 2 divided doses) if: 1, 3, 2
- No improvement after 72 hours of amoxicillin therapy
- Symptoms worsen at any time during treatment
- The child has moderate to severe illness at presentation
- Recent antibiotic exposure (within 4-6 weeks)
The clavulanate component provides essential coverage against β-lactamase-producing organisms (H. influenzae and M. catarrhalis), which account for approximately 40% of pediatric bacterial sinusitis cases 1
Critical Diagnostic Considerations
Antibiotics should only be prescribed when acute bacterial sinusitis is confirmed by one of three patterns: 3
- Persistent symptoms ≥10 days without improvement (nasal discharge, daytime cough)
- Severe symptoms for ≥3 consecutive days (fever ≥39°C with purulent nasal discharge)
- "Double sickening" - worsening symptoms after initial improvement from a viral URI
Most acute rhinosinusitis (98-99.5%) is viral and resolves spontaneously within 7-10 days without antibiotics 3
Alternative for Children Unable to Tolerate Oral Medication
Ceftriaxone 50 mg/kg IM or IV as a single dose can be used for children who are vomiting or unable to take oral medications 1, 2
- Transition to oral amoxicillin if improvement occurs within 24 hours
- This is a bridging strategy, not definitive therapy
Important Caveats
Reassess at 72 hours: If no improvement or worsening occurs, switch to amoxicillin-clavulanate or consider alternative diagnosis 1, 3, 2
Avoid these antibiotics due to high resistance rates: 1, 3
- Azithromycin and other macrolides (20-25% resistance)
- Trimethoprim-sulfamethoxazole (20-25% resistance)
- First-generation cephalosporins
Evidence regarding antibiotic benefit is mixed: Studies in children show conflicting results, with some demonstrating no benefit of amoxicillin over placebo for post-viral sinusitis 1, 5, while others show significant benefit with high-dose amoxicillin-clavulanate 6. However, when bacterial sinusitis is clinically diagnosed using strict criteria (persistent symptoms ≥10 days, severe symptoms, or double sickening), antibiotics reduce treatment failures from 68% to 14% 6
Adjunctive therapies that may help: 3
- Intranasal corticosteroids (reduce mucosal inflammation)
- Saline nasal irrigation
- Analgesics (acetaminophen or ibuprofen) for pain and fever