What are the first-line antibiotics for sinusitis?

First-Line Antibiotics for Sinusitis

Amoxicillin is the first-line antibiotic for acute bacterial sinusitis in most patients, dosed at 500 mg twice daily for adults or 45 mg/kg/day in 2 divided doses for children, for 10-14 days. 1, 2

When to Use Standard-Dose Amoxicillin

• Standard-dose amoxicillin (500 mg twice daily for adults; 45 mg/kg/day for children) is appropriate for uncomplicated acute bacterial sinusitis without recent antibiotic exposure or high-risk factors. 1, 2
• This regimen targets the three most common pathogens: Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis. 2, 3

When to Escalate to High-Dose Amoxicillin or Amoxicillin-Clavulanate

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

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

• The clavulanate component provides coverage against β-lactamase-producing H. influenzae (10-42% resistance to amoxicillin alone) and M. catarrhalis (nearly 100% β-lactamase positive). 1, 2

• Recent evidence shows no significant benefit of high-dose over standard-dose amoxicillin-clavulanate in adults with clinically diagnosed acute sinusitis, though high-dose immediate-release formulations may provide more rapid symptom improvement at the cost of increased diarrhea (15.8% vs 4.8%). 4, 5

First-Line Options for Penicillin-Allergic Patients

• For non-severe penicillin allergy (rash, mild reactions), second- or third-generation cephalosporins are safe and effective first-line alternatives: 1, 2

  • Cefuroxime-axetil 1
  • Cefpodoxime-proxetil 1, 2
  • Cefdinir 1, 2
  • Cefprozil 1

• The risk of cross-reactivity between penicillins and second/third-generation cephalosporins is negligible for non-Type I hypersensitivity reactions. 1

• For severe Type I penicillin allergy (anaphylaxis), respiratory fluoroquinolones are the preferred alternative: 1

  • Levofloxacin 500 mg once daily for 10-14 days 1, 6
  • Moxifloxacin 400 mg once daily for 10 days 1

Antibiotics to Avoid as First-Line Therapy

• Azithromycin and other macrolides should NOT be used as first-line therapy due to resistance rates of 20-25% for both S. pneumoniae and H. influenzae. 1, 7, 3

• Trimethoprim-sulfamethoxazole should be avoided due to high resistance rates (20-25%). 1

• First-generation cephalosporins (e.g., cephalexin) are inappropriate due to inadequate coverage against H. influenzae, with nearly 50% of strains being β-lactamase producing. 1

• Doxycycline has limited activity against H. influenzae and a predicted bacteriologic failure rate of 20-25%, making it suboptimal when better alternatives exist. 1

Treatment Duration

• The standard duration is 10-14 days, or until symptom-free for 7 days. 1, 2, 3
• Some studies suggest 5-7 day courses may have comparable efficacy with fewer side effects, though 10-14 days remains the guideline recommendation. 1, 8

When to Reassess and Switch Antibiotics

• Reassess patients at 3-5 days: if no improvement, switch to a different antibiotic or re-evaluate the diagnosis. 1
• At 7 days: confirm the diagnosis if symptoms persist or worsen. 1
• For treatment failure after 3-5 days, switch to high-dose amoxicillin-clavulanate (if not already used) or a respiratory fluoroquinolone. 1

Critical Diagnostic Criteria Before Starting Antibiotics

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

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

• 98-99.5% of acute rhinosinusitis is viral and resolves spontaneously within 7-10 days without antibiotics. 1

Adjunctive Therapies

• Intranasal corticosteroids (mometasone, fluticasone, budesonide) twice daily are strongly recommended as adjunctive therapy to reduce mucosal inflammation and improve symptom resolution. 1
• Analgesics (acetaminophen, NSAIDs) for pain relief 1
• Saline nasal irrigation for symptomatic relief 1
• Decongestants (systemic or topical) as needed 1

Common Pitfalls to Avoid

• Do not prescribe antibiotics for symptoms lasting <10 days unless severe symptoms are present. 1
• Do not use mucus color alone to determine antibiotic need, as color reflects neutrophils, not bacteria. 1
• Do not continue ineffective therapy beyond 3-5 days without reassessment. 1
• Reserve fluoroquinolones for treatment failures or severe penicillin allergy to prevent resistance development. 1, 6