What is the appropriate treatment for a bacterial sinus infection with amoxicillin (amoxicillin)?

Treatment of Acute Bacterial Sinusitis with Amoxicillin

Amoxicillin is the first-line antibiotic for acute bacterial sinusitis in adults at 500 mg twice daily for mild disease or 875 mg twice daily for moderate disease, with treatment duration of 7-10 days. 1, 2

When to Start Antibiotics

Not all sinus infections require antibiotics. Initiate antibiotic therapy only when patients meet specific diagnostic criteria:

• Persistent symptoms lasting >10 days without improvement (nasal discharge, congestion, facial pain/pressure, or cough) 2, 3
• Severe onset with high fever (≥39°C/102°F) and purulent nasal discharge for 3-4 consecutive days 2, 3
• Worsening course after initial improvement ("double-sickening"): respiratory symptoms that worsen after 5-7 days of improvement 2, 3
• Unilateral sinus tenderness and worsening symptoms when bending forward increase likelihood of bacterial infection 4

For mild-to-moderate symptoms without these criteria, symptomatic treatment with decongestants and analgesics is preferred initially, as most patients improve without antibiotics. 4

First-Line Amoxicillin Dosing

Standard-dose amoxicillin:

• Adults: 500 mg twice daily for uncomplicated cases OR 875 mg twice daily for moderate disease 1, 2
• Children: 45 mg/kg/day divided into 2 doses 1, 2
• Duration: 7-10 days, or until symptom-free for 7 days (typically 10-14 days total) 1, 2

High-dose amoxicillin (80-90 mg/kg/day for children, 875 mg twice daily for adults) is indicated when:

• Age <2 years 1, 2
• Daycare attendance 1, 2
• Recent antibiotic use within 4-6 weeks 1, 2
• Geographic areas with high prevalence of penicillin-resistant S. pneumoniae (>10-15% resistance) 1, 2

When to Use Amoxicillin-Clavulanate Instead

Switch to amoxicillin-clavulanate 875/125 mg twice daily for adults (or 80-90 mg/kg/day of amoxicillin component for children) when: 1, 2

• No improvement after 3-5 days of standard amoxicillin 1
• Risk factors for β-lactamase-producing organisms (H. influenzae, M. catarrhalis): recent antibiotic exposure, daycare attendance, age <2 years 1, 2
• More severe infection at presentation 1

The clavulanate component provides coverage against β-lactamase-producing bacteria, which account for 10-42% of H. influenzae and nearly 100% of M. catarrhalis isolates. 2

Penicillin-Allergic Patients

For documented penicillin allergy, use second- or third-generation cephalosporins as first-line alternatives: 1, 2

• Cefdinir, cefuroxime, or cefpodoxime are appropriate alternatives 1, 2
• Cross-reactivity risk with second- and third-generation cephalosporins is negligible, even in documented penicillin allergy 1

Avoid azithromycin and other macrolides due to 20-25% resistance rates of S. pneumoniae and H. influenzae. 1, 2

Treatment Failure Protocol

If no improvement after 3-5 days (adults) or 72 hours (children), reassess and switch antibiotics: 1, 2

• Second-line option: Amoxicillin-clavulanate 875/125 mg twice daily if not already used 1
• Third-line option: Respiratory fluoroquinolones (levofloxacin 500-750 mg once daily or moxifloxacin) for treatment failures or complicated sinusitis involving frontal, ethmoidal, or sphenoidal sinuses 1

Fluoroquinolones provide 90-92% clinical efficacy and excellent coverage against multi-drug resistant S. pneumoniae, but should be reserved to prevent resistance development. 1

Adjunctive Therapies

Intranasal corticosteroids are recommended as adjunctive therapy to antibiotics in both acute and chronic sinusitis. 1

Short-term oral corticosteroids (e.g., dexamethasone 4 mg) may be considered for acute hyperalgic sinusitis (severe facial pain) or marked mucosal edema when combined with appropriate antibiotics. 1

Supportive measures include adequate hydration, analgesics, warm facial packs, and sleeping with head elevated. 1

Critical Pitfalls to Avoid

• Do not prescribe antibiotics for symptoms <7 days unless severe onset criteria are met—most cases are viral 4, 2
• Ensure adequate treatment duration (minimum 7-10 days) to prevent relapse; do not stop when symptoms improve 1, 2
• Avoid azithromycin as first-line therapy due to high resistance rates (20-25%) 1, 2
• Reserve fluoroquinolones for treatment failures or complicated sinusitis to prevent resistance 1
• Reassess at 3-5 days if no improvement—do not continue ineffective therapy 1, 2
• Imaging is not recommended for uncomplicated acute bacterial sinusitis diagnosis 4, 2

Red Flags Requiring Immediate Specialist Referral

Seek urgent imaging and specialist consultation for: 5

• Periorbital or orbital swelling with proptosis 5
• Impaired extraocular muscle function 5
• Severe headache with photophobia 5
• Seizures or focal neurologic findings 5

These suggest potential complications such as orbital cellulitis, cavernous sinus thrombosis, or intracranial extension requiring immediate intervention.