What is the recommended dosing of amoxicillin (amoxicillin) for the treatment of sinusitis?

Amoxicillin Dosing for Sinusitis

For adults with acute bacterial sinusitis, start with amoxicillin 500 mg three times daily (or 875 mg twice daily) for 5-7 days, reserving high-dose amoxicillin-clavulanate (2000 mg/125 mg twice daily) for patients with recent antibiotic use, moderate-to-severe disease, or risk factors for resistant organisms. 1, 2

Standard First-Line Dosing

Amoxicillin remains the preferred initial antibiotic due to its safety, efficacy, low cost, and narrow microbiologic spectrum. 1

• Standard adult dose: 500 mg three times daily (every 8 hours) for 5-7 days 1, 2, 3
• Alternative regimen: 875 mg twice daily (every 12 hours) for 5-7 days 1, 3
• Both regimens provide equivalent clinical efficacy 4

The shorter 5-7 day duration is now preferred over traditional 10-14 day courses, as multiple trials demonstrate similar success rates with reduced antibiotic exposure 1. However, some guidelines still recommend continuing treatment until the patient is symptom-free for 7 days, which typically results in a 10-14 day total course 1, 3.

When to Escalate to Amoxicillin-Clavulanate

Consider amoxicillin-clavulanate instead of amoxicillin alone when specific risk factors for resistant organisms are present. 1

High-Risk Factors Requiring Amoxicillin-Clavulanate:

• Recent antibiotic use (within past 4-6 weeks) 1
• Moderate-to-severe symptoms or protracted symptoms 1
• Recent hospitalization or healthcare contact 1
• Age >65 years 1
• Immunocompromised status 1
• Chronic comorbidities (diabetes, cardiac, hepatic, or renal disease) 1
• Close contact with daycare facilities 1
• Smoking or household smoker 1
• Geographic areas with high prevalence (>10%) of penicillin-nonsusceptible S. pneumoniae 1

Amoxicillin-Clavulanate Dosing:

• High-dose regimen: 2000 mg amoxicillin/125 mg clavulanate twice daily 1, 2
• Standard-dose alternative: 875 mg/125 mg twice daily or 500 mg/125 mg three times daily 1

The high-dose formulation is specifically designed to cover penicillin-nonsusceptible S. pneumoniae and β-lactamase-producing H. influenzae and M. catarrhalis 1.

Treatment Response Assessment

Evaluate clinical response after 3-5 days of therapy. 1, 3

• If improving: Continue current antibiotic until symptom-free for 7 days (typically 10-14 days total) 1, 3
• If no improvement or worsening: Switch to high-dose amoxicillin-clavulanate, a respiratory fluoroquinolone, or cefuroxime axetil 1

This early reassessment is critical—failure to switch antibiotics at 72 hours when patients aren't improving delays appropriate therapy and risks complications 1, 3.

Penicillin-Allergic Patients

For patients with documented penicillin allergy:

• Doxycycline or respiratory fluoroquinolone (levofloxacin 500 mg daily or moxifloxacin 400 mg daily) 1
• Non-type I hypersensitivity: Combination of clindamycin plus third-generation cephalosporin (cefixime or cefpodoxime) 1

Avoid macrolides (azithromycin, clarithromycin) and trimethoprim-sulfamethoxazole as first-line therapy due to high resistance rates: >40% for macrolides against S. pneumoniae and 50% for TMP-SMX 1.

Pediatric Dosing

• Standard dose: 45 mg/kg/day divided twice daily 1
• High-dose: 80-90 mg/kg/day divided twice daily (maximum 2000 mg/dose) 1
• High-dose formulations are preferred in children due to higher rates of antibiotic resistance in daycare settings 1

Critical Pitfalls to Avoid

Do not prescribe antibiotics for viral upper respiratory infections or post-viral rhinosinusitis without bacterial features. 1, 3 Studies demonstrate that antibiotics provide minimal benefit over placebo in post-viral sinusitis, with increased adverse events 1, 5. Bacterial sinusitis should be suspected only when:

• Symptoms persist >10 days without improvement 1
• Severe symptoms (fever ≥39°C, purulent discharge, facial pain) for ≥3-4 consecutive days 1
• "Double worsening" (initial improvement followed by worsening) 1

Complete the full antibiotic course even if symptoms improve early. 1, 5 Premature discontinuation risks incomplete bacterial eradication and relapse 1, 5.

Recognize that high-dose amoxicillin-clavulanate increases diarrhea risk. Recent trials show severe diarrhea rates of 7-16% with high-dose formulations versus 5-7% with standard doses 6, 7. The clinical benefit of high-dose therapy may not outweigh this risk in all patients 7.

Adjunctive Therapies

Recommend intranasal saline irrigation and intranasal corticosteroids as adjuncts to antibiotic therapy. 2 These provide symptomatic relief and may enhance antibiotic efficacy 1, 2.

Avoid topical/oral decongestants and antihistamines—they lack proven benefit in acute bacterial sinusitis 2.