Amoxicillin Dosing for Acute Bacterial Sinusitis in Adults
For otherwise healthy adults with acute bacterial sinusitis, prescribe amoxicillin 500 mg three times daily OR 875 mg twice daily for 5-7 days. 1, 2
First-Line Antibiotic Selection
Amoxicillin remains the drug of choice for uncomplicated acute bacterial sinusitis due to its effectiveness, safety, low cost, and narrow microbiologic spectrum 3, 1. The most recent 2025 AAO-HNS guideline now recommends amoxicillin with or without clavulanate as first-line therapy, representing a shift from the 2015 guideline that recommended amoxicillin alone 2.
Standard Dosing Regimens
- Amoxicillin alone: 500 mg three times daily OR 875 mg twice daily 4, 5
- Duration: 5-7 days is sufficient 1, 2
The evidence shows that shorter durations (5-7 days) are as effective as traditional 10-14 day courses, with the added benefit of reduced adverse events 1. A 2026 observational study of over 500,000 patients found no difference in treatment failure between standard-dose amoxicillin-clavulanate and amoxicillin alone 6.
When to Use High-Dose Amoxicillin-Clavulanate
Consider high-dose amoxicillin-clavulanate (2 g amoxicillin/125 mg clavulanate twice daily) if the patient has:
- Antibiotic use within the past month
- Moderate to severe symptoms or protracted illness
- Geographic area with >10% penicillin-nonsusceptible S. pneumoniae
- Age >65 years
- Recent hospitalization
- Immunocompromised state
- Diabetes or other significant comorbidities
- Close contact with daycare facilities
- Smoking history 1, 2
However, a 2021 randomized trial found no benefit of high-dose over standard-dose amoxicillin-clavulanate for acute sinusitis 7, and the 2026 observational study showed amoxicillin-clavulanate was associated with higher rates of secondary infections (yeast infections and C. difficile) without improved efficacy 6.
Penicillin-Allergic Patients
For patients with true penicillin allergy:
Avoid macrolides and trimethoprim-sulfamethoxazole due to high resistance rates (>40% for macrolides, 50% for TMP-SMX against S. pneumoniae) 1.
Treatment Duration and Follow-Up
The optimal duration is 5-7 days for uncomplicated cases 1, 2. Some older guidelines suggested treating until 7 days after symptom resolution (typically 10-14 days total) 3, but more recent evidence supports shorter courses to minimize adverse events while maintaining efficacy 1.
Reassess at 3-5 days: If no improvement or worsening symptoms, consider switching to high-dose amoxicillin-clavulanate or an alternative agent 3.
Common Pitfalls
Overprescribing antibiotics: Many cases of acute rhinosinusitis are viral and do not require antibiotics. The 2025 guideline now extends watchful waiting as an option for all patients with uncomplicated ABRS, regardless of severity 2.
Excessive duration: Most antibiotics are prescribed for >7 days despite evidence supporting shorter courses 8. This increases adverse events without improving outcomes.
Unnecessary use of broad-spectrum agents: Fluoroquinolones should not be first-line therapy due to comparable outcomes with amoxicillin but higher adverse event rates 1.
Geographic variation: Rural areas and urgent care settings show lower rates of guideline-concordant prescribing 8, highlighting the need for targeted stewardship efforts.