Amoxicillin Dosing and Duration for Acute Bacterial Sinusitis
For an adult with acute bacterial sinusitis and no penicillin allergy, prescribe amoxicillin 500 mg three times daily (every 8 hours) for 5-7 days, taken at the start of meals. 1, 2, 3
Standard Dosing Options
Two evidence-based regimens are available:
- 500 mg three times daily (every 8 hours) for 5-7 days - This is the most commonly recommended first-line option 4, 1, 2, 3
- 875 mg twice daily (every 12 hours) for 5-7 days - An alternative with equivalent efficacy 1, 2, 3
Both regimens should be taken at the start of a meal to minimize gastrointestinal side effects 5
Treatment Duration: Shorter is Better
The recommended duration is 5-7 days for uncomplicated acute bacterial sinusitis in adults. 2, 3 This represents a significant shift from older 10-14 day recommendations. The Infectious Diseases Society of America now supports this shorter duration based on weak recommendation with low-moderate quality evidence 2. Multiple clinical trials demonstrate that 5-day courses have equivalent or superior efficacy compared to traditional 10-14 day regimens 6.
However, treatment should continue until the patient has been symptom-free for approximately 7 days if symptoms persist beyond the initial 5-7 day course 1, 3
Critical Reassessment Point
Evaluate treatment response at 3-5 days. 1, 2 At this checkpoint:
- If symptoms worsen or fail to improve, consider switching to amoxicillin-clavulanate (high-dose: 2000mg/125mg twice daily or standard 875mg/125mg twice daily) 2, 7
- If partial response occurs, continue the antibiotic for the full course 2
- One study showed that high-dose immediate-release amoxicillin-clavulanate (1750mg twice daily) led to more rapid improvement at day 3 (52.4% vs 34.4%) compared to standard dosing, though this came with increased severe diarrhea (15.8% vs 4.8%) 7
When NOT to Use Antibiotics
Do not prescribe amoxicillin for viral or post-viral rhinosinusitis. 1, 3 Multiple high-quality placebo-controlled trials demonstrate that antibiotics provide no benefit for post-viral acute rhinosinusitis, with no difference in cure rates at 14 days and increased adverse events 4, 1, 8. The European Position Paper on Rhinosinusitis found that neither antibiotics nor topical steroids alone or in combination were effective for acute sinusitis in primary care 8.
Antibiotics are only indicated when bacterial sinusitis is confirmed by:
- Symptoms lasting ≥10 days without improvement 4
- Severe symptoms (purulent discharge AND facial pain) for at least 3-4 consecutive days 4
- "Double sickening" - worsening after initial improvement 4
Adjunctive Therapies to Recommend
Prescribe intranasal saline irrigation and intranasal corticosteroids as adjunctive treatments. 2 The Infectious Diseases Society of America recommends these based on weak recommendation with low-moderate quality evidence 2. Notably, nasal corticosteroids may be more effective than amoxicillin for symptom relief in some patients with post-viral sinusitis 1.
Avoid topical or oral decongestants and antihistamines - these are not recommended by current guidelines 2
Common Pitfalls to Avoid
Treating viral upper respiratory infections with antibiotics - This is the most common error and contributes to antibiotic resistance 1, 3. Studies consistently show antibiotics do not reduce symptom burden in post-viral rhinosinusitis 3, 8
Failing to reassess at 3-5 days - This delays necessary changes in therapy when initial treatment fails 1, 2
Prescribing unnecessarily long courses - The traditional 10-14 day course is not supported by strong evidence for uncomplicated cases 2, 6
Stopping antibiotics when symptoms improve - If antibiotics are indicated, complete the full 5-7 day course to prevent incomplete eradication and relapse 3
Special Considerations for Renal Impairment
For patients with severe renal impairment (GFR <30 mL/min), do NOT use the 875mg dose 5. Adjust dosing as follows: