What are the recommended antibiotic treatments and dosing for acute bacterial sinusitis?

Antibiotic Treatment for Acute Bacterial Sinusitis

Amoxicillin with or without clavulanate is the first-line antibiotic for acute bacterial sinusitis in adults, dosed at 500-875 mg twice daily (or 500 mg three times daily) for 5-10 days. 1, 2, 3

When to Start Antibiotics

Not all sinusitis requires antibiotics. Diagnose acute bacterial rhinosinusitis (ABRS) when patients present with one of three patterns:

• Persistent symptoms: Nasal discharge or daytime cough lasting >10 days without improvement
• Severe onset: Fever ≥102.2°F (39°C) with purulent nasal discharge for ≥3 consecutive days
• Worsening course: Initial improvement followed by worsening symptoms 4, 5, 2

Watchful waiting without antibiotics is appropriate for uncomplicated ABRS if you can ensure follow-up within 7 days. Start antibiotics only if symptoms fail to improve by day 7 or worsen at any time. 1, 2

First-Line Antibiotic Regimens

Standard Dosing (Most Adults)

Amoxicillin alone:

• 500 mg three times daily, OR
• 875 mg twice daily
• Duration: 5-10 days 6, 1, 2

Amoxicillin-clavulanate (preferred when resistance suspected):

• 875 mg-125 mg twice daily
• Duration: 5-10 days 1, 2

The 2026 JAMA study found no difference in treatment failure between amoxicillin-clavulanate and amoxicillin alone (3.0% vs 3.1%), but amoxicillin-clavulanate had higher rates of yeast infections (1.1% vs 0.8%) and C. difficile infections (0.04% vs 0.02%). 3 This supports using amoxicillin alone as the preferred first-line agent unless resistance is a concern.

High-Dose Regimens (When Resistance Suspected)

Use high-dose therapy if the patient:

• Attended daycare recently (children)
• Used antibiotics in past 4-6 weeks
• Lives in areas with >10% penicillin-resistant S. pneumoniae
• Has moderate-to-severe disease 6, 5

High-dose amoxicillin-clavulanate:

• Adults: 2000 mg (amoxicillin component) every 12 hours (not exceeding 2 g per dose) 6
• Children: 80-90 mg/kg/day of amoxicillin component with 6.4 mg/kg/day clavulanate in 2 divided doses 5, 7

Penicillin Allergy Alternatives

For non-severe penicillin allergy:

• Cefuroxime axetil, cefpodoxime proxetil, or cefdinir 6, 8
• Recent evidence shows cross-reactivity risk with 2nd/3rd generation cephalosporins is negligible 5

For severe (Type 1) penicillin allergy:

• Levofloxacin or moxifloxacin (respiratory fluoroquinolones) 6, 7
• Avoid trimethoprim-sulfamethoxazole and azithromycin due to high resistance rates in S. pneumoniae and H. influenzae 4, 9

Treatment Failure Management

If no improvement after 3-5 days or worsening at any time, reassess the diagnosis and switch antibiotics: 6, 1

Second-line options:

• High-dose amoxicillin-clavulanate (if not used initially)
• Cefuroxime, cefpodoxime, or cefdinir
• Respiratory fluoroquinolones (levofloxacin, moxifloxacin) 6, 7

For persistent failure after 21-28 days:

• Consider anaerobic coverage: add clindamycin or metronidazole to broad-spectrum agent
• Obtain CT imaging
• Refer to otolaryngology or allergy/immunology 6

Special Situations

Frontal, ethmoidal, or sphenoidal sinusitis:

• More serious; consider starting with respiratory fluoroquinolones (levofloxacin, moxifloxacin) or high-dose amoxicillin-clavulanate 7

Severe/toxic appearance:

• IV ceftriaxone 50 mg/kg (up to 2 g) once daily, then switch to oral after clinical improvement 4, 5

Chronic rhinosinusitis:

• Do not use empiric antibiotics solely to satisfy third-party requirements for surgery or imaging 2
• Antibiotics have limited role; focus on intranasal corticosteroids and addressing underlying inflammation 6, 10

Adjunctive Therapies

• Intranasal corticosteroids: Beneficial as monotherapy for mild-moderate cases or as adjunct to antibiotics 6, 11
• Nasal saline irrigation: Recommended; safe and effective 9, 11
• Oral decongestants: May provide symptomatic relief but limited evidence 6
• Avoid topical decongestants >3 days (risk of rebound congestion) 9

Common Pitfalls

• Over-diagnosing bacterial sinusitis: Most cases are viral and resolve without antibiotics. Wait 10 days before diagnosing ABRS unless severe symptoms present. 6, 2
• Using broad-spectrum antibiotics first-line: This drives resistance. Start narrow (amoxicillin) and escalate only if needed. 1, 3
• Treating chronic rhinosinusitis like acute: Chronic disease requires different management focused on inflammation, not routine antibiotics. 2, 10
• Ignoring treatment failure: If no improvement by day 7, don't continue the same antibiotic—reassess and change therapy. 6, 1