First-Line Antibiotic for Uncomplicated Acute Bacterial Sinusitis in Adults
For adults with uncomplicated acute bacterial sinusitis, prescribe amoxicillin with or without clavulanate for 5-10 days; for patients with severe penicillin allergy, use doxycycline or a respiratory fluoroquinolone (levofloxacin or moxifloxacin). 1, 2
Recommended Dosing Regimens
Standard First-Line Therapy
High-Dose Therapy (for resistant organisms)
Use high-dose amoxicillin-clavulanate when patients have:
- Recent antibiotic use (within past month)
- Moderate to severe symptoms
- Age >65 years
- Failed prior antibiotic therapy
- Geographic areas with high penicillin-resistant S. pneumoniae (>10%)
High-dose regimen: 2000 mg amoxicillin with 125 mg clavulanate twice daily (or 90 mg/kg amoxicillin component, not to exceed 2 g every 12 hours) 3, 1
Severe Penicillin Allergy Alternatives
- Doxycycline: Standard adult dosing (typically 100 mg twice daily)
- Levofloxacin: 500 mg once daily 3
- Moxifloxacin: Respiratory fluoroquinolone dosing 4
Critical Decision Points
When to Prescribe Antibiotics
Only prescribe antibiotics when patients meet bacterial criteria (not viral):
- Persistent symptoms >10 days without improvement, OR
- Severe symptoms: fever >39°C (102°F) with purulent nasal discharge or facial pain for ≥3 consecutive days, OR
- "Double sickening": worsening symptoms after initial improvement 4
Watchful Waiting Option
Watchful waiting without antibiotics is appropriate for ALL patients with uncomplicated ABRS, regardless of severity, when follow-up is assured within 7 days 1, 2, 5. This approach recognizes that:
- Number needed to treat is 18 for one additional cure
- Number needed to harm from adverse effects is 8
- Most patients improve spontaneously 4
Amoxicillin vs. Amoxicillin-Clavulanate Controversy
There is divergence in guideline recommendations:
2012 IDSA guidelines (referenced in 2016 ACP/CDC): Prefer amoxicillin-clavulanate due to resistance concerns for H. influenzae and M. catarrhalis 4
2015 AAO-HNS guidelines: Either amoxicillin alone OR amoxicillin-clavulanate acceptable, with amoxicillin preferred for cost-effectiveness and narrow spectrum 1, 2, 1
2025 AAO-HNS update: Changed to recommend amoxicillin "with or without clavulanate" as first-line 5
The most recent high-quality guideline (2025) gives flexibility for either option, though amoxicillin-clavulanate should be strongly considered when risk factors for resistance are present (see Table 7 factors above) 1.
Treatment Duration
5-10 days is the recommended range 1, 2, 1. Shorter courses (5-7 days) have comparable efficacy with fewer adverse effects, though 10-14 days has been traditional 3. The evidence does not consistently favor 10 days over shorter courses.
Common Pitfalls to Avoid
Do NOT prescribe antibiotics for viral rhinosinusitis (symptoms <10 days that are improving) - this represents the vast majority of "sinusitis" diagnoses 4
Do NOT use macrolides as first-line therapy - they are commonly prescribed but not recommended due to inferior coverage 4
Do NOT use first-generation cephalosporins (cephalexin) - inadequate H. influenzae coverage 3
Do NOT use cefixime or ceftibuten - poor activity against S. pneumoniae 3
Avoid cephalosporins in severe penicillin allergy - cross-reactivity risk exists 3
Adjunctive Therapy
Recommend alongside antibiotics:
- Intranasal saline irrigation
- Intranasal corticosteroids (may decrease antibiotic need)
- Analgesics for pain
- Adequate hydration 3, 4
When to Reassess
Patients should contact you if:
- No improvement after 3-5 days of antibiotics
- Worsening symptoms at any time
- High fever or severe headache develops 3
For treatment failure, switch to high-dose amoxicillin-clavulanate, cefuroxime, cefpodoxime, or respiratory fluoroquinolone 3.