What are the first-line antibiotics for sinus infection?

First-Line Antibiotics for Acute Bacterial Sinusitis

Amoxicillin is the first-line antibiotic for most adults and children with uncomplicated acute bacterial sinusitis, dosed at 500 mg twice daily for adults (or 875 mg twice daily for moderate disease) and 45 mg/kg/day in 2 divided doses for children, with treatment duration of 5-10 days. 1, 2

When to Use Standard-Dose vs. High-Dose Amoxicillin

Standard-dose amoxicillin (500 mg twice daily for adults; 45 mg/kg/day for children) is appropriate for: 2

• Uncomplicated disease without recent antibiotic exposure
• Areas with low prevalence of resistant S. pneumoniae
• Patients ≥2 years old not in daycare 2

High-dose amoxicillin or amoxicillin-clavulanate (875 mg twice daily for adults; 80-90 mg/kg/day for children) should be used for: 1, 2

• Age <2 years
• Daycare attendance
• Recent antibiotic use within 4-6 weeks
• Areas with high prevalence of penicillin-resistant S. pneumoniae (>10-15%) 2
• Moderate-to-severe disease 1

The rationale for escalating to amoxicillin-clavulanate in high-risk situations is coverage against β-lactamase-producing H. influenzae (10-42% resistance) and M. catarrhalis (nearly 100% resistance). 2

Treatment Duration: 5-10 Days is Sufficient

Treat for 5-10 days, with most guidelines recommending treatment until symptom-free for 7 days (typically 10-14 days total). 1, 2 Recent evidence demonstrates that 5-day courses have comparable efficacy to 10-day regimens with fewer adverse effects. 1 The traditional 10-14 day recommendation lacks strong scientific rationale, and shorter courses reduce antibiotic exposure while maintaining clinical success rates of 72-80%. 3, 4

Penicillin-Allergic Patients: Use Cephalosporins

For documented penicillin allergy, second- or third-generation cephalosporins are first-line alternatives due to negligible cross-reactivity risk: 1, 2

• Cefdinir (preferred third-generation option) 2
• Cefuroxime (second-generation option) 2
• Cefpodoxime (third-generation with superior H. influenzae activity) 2

The risk of serious allergic reactions to second- and third-generation cephalosporins in penicillin-allergic patients is negligible, making these safe and effective alternatives. 1

When NOT to Use Certain Antibiotics

Avoid these antibiotics as first-line therapy: 1

• Azithromycin and macrolides: 20-25% resistance rates for S. pneumoniae and H. influenzae make them inappropriate 1
• Trimethoprim-sulfamethoxazole: High resistance rates (50% for S. pneumoniae, 27% for H. influenzae) 1
• Fluoroquinolones (levofloxacin, moxifloxacin): Reserve as second-line therapy to prevent resistance development 1, 5

Confirming Bacterial vs. Viral Sinusitis Before Prescribing

Only prescribe antibiotics when bacterial sinusitis is confirmed by one of three patterns: 1

1. Persistent symptoms ≥10 days without improvement
2. Severe symptoms (fever ≥39°C with purulent discharge) for ≥3 consecutive days
3. "Double sickening" (worsening after initial improvement from viral URI)

This is critical because 98-99.5% of acute rhinosinusitis is viral and resolves spontaneously within 7-10 days without antibiotics. 1 Antibiotics are prescribed in 81-92% of cases despite only 0.5-2% having bacterial etiology, contributing to unnecessary adverse effects and antimicrobial resistance. 1

Treatment Failure Protocol: Reassess at 3-5 Days

If no improvement after 72 hours (pediatrics) or 3-5 days (adults), switch to amoxicillin-clavulanate 875 mg/125 mg twice daily (or 90 mg/kg/day amoxicillin component for children). 1, 2 This provides coverage against β-lactamase-producing organisms and drug-resistant S. pneumoniae. 1

If amoxicillin-clavulanate fails, escalate to respiratory fluoroquinolones (levofloxacin 500 mg once daily or moxifloxacin 400 mg once daily for 10 days), which achieve 90-92% clinical efficacy. 1, 6

Adjunctive Therapies to Enhance Outcomes

Intranasal corticosteroids (mometasone, fluticasone, budesonide twice daily) are strongly recommended as adjunctive therapy, reducing mucosal inflammation and improving symptom resolution with strong evidence from multiple RCTs. 1 These provide symptomatic relief but have no antibacterial activity, so never give systemic corticosteroids without antibiotics when bacterial sinusitis is suspected. 1

Critical Pitfalls to Avoid

• Do not prescribe antibiotics for viral rhinosinusitis lasting <10 days unless severe symptoms are present 1
• Do not use mucus color alone to determine antibiotic need—color reflects neutrophils, not bacteria 1
• Do not continue ineffective therapy beyond 72 hours (pediatrics) or 3-5 days (adults) without reassessment 1, 2
• Complete the full antibiotic course even after symptoms improve to prevent relapse 1