What is the first‑line antibiotic regimen for acute bacterial sinusitis in otherwise healthy adults and children?

First-Line Antibiotics for Acute Bacterial Sinusitis

Amoxicillin-clavulanate 875 mg/125 mg twice daily for 5–10 days is the preferred first-line antibiotic for adults with acute bacterial sinusitis, providing 90–92% predicted clinical efficacy against the major pathogens. 1

Confirm the Diagnosis Before Prescribing

Before initiating antibiotics, verify that the patient meets at least one of three diagnostic criteria for acute bacterial rhinosinusitis (ABRS):

• Persistent symptoms ≥10 days without improvement—purulent nasal discharge plus either nasal obstruction or facial pain/pressure/fullness. This is the most common scenario. 1, 2
• Severe symptoms ≥3–4 consecutive days—fever ≥39°C with purulent nasal discharge and facial pain at illness onset. 1, 2
• "Double sickening"—initial improvement from a viral URI followed by new-onset fever, worsening nasal discharge, or markedly increased cough within 10 days. 1, 2

Do not prescribe antibiotics for symptoms <10 days unless the severe criteria above are met—approximately 98–99.5% of acute rhinosinusitis is viral and resolves spontaneously within 7–10 days. 1, 2

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First-Line Antibiotic Regimen

Standard Dosing for Most Adults

• Amoxicillin-clavulanate 875 mg/125 mg orally twice daily for 5–10 days (or until symptom-free for 7 consecutive days, typically 10–14 days total). 1, 2
• The clavulanate component is essential because 30–40% of Haemophilus influenzae and 90–100% of Moraxella catarrhalis produce β-lactamase. 1
• Recent evidence supports shorter 5–7 day courses with comparable efficacy and fewer adverse effects. 1, 3

High-Dose Regimen for Specific Risk Factors

Use high-dose amoxicillin-clavulanate 2 g/125 mg twice daily when any of the following are present: 1, 2

• Recent antibiotic use within the past 4–6 weeks
• Age >65 years
• Daycare attendance (or close contact with daycare children)
• Moderate-to-severe symptoms
• Comorbidities (diabetes, chronic cardiac/hepatic/renal disease)
• Immunocompromised state
• Smoking or exposure to secondhand smoke

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Alternatives for Penicillin-Allergic Patients

Non-Severe (Non-Type I) Penicillin Allergy

• Second- or third-generation cephalosporins for 10 days—cross-reactivity with penicillin is negligible (<1%). 1, 2
  • Options: cefuroxime-axetil, cefpodoxime-proxetil, cefdinir, or cefprozil. 1

Severe (Type I/Anaphylactic) Penicillin Allergy

• Respiratory fluoroquinolones provide 90–92% predicted efficacy against multidrug-resistant Streptococcus pneumoniae and β-lactamase-producing organisms: 1, 2
  • Levofloxacin 500 mg once daily for 10–14 days, or
  • Moxifloxacin 400 mg once daily for 10 days
• Reserve fluoroquinolones for severe allergy or treatment failure to limit resistance development. 1, 2

Suboptimal Alternative

• Doxycycline 100 mg once daily for 10 days offers lower efficacy (77–81%) with a 20–25% bacteriologic failure rate due to limited H. influenzae coverage. Use only when cephalosporins and fluoroquinolones are contraindicated. 1
• Contraindicated in children <8 years due to tooth enamel discoloration risk. 1

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Pediatric Dosing

• Standard-dose amoxicillin: 45 mg/kg/day divided twice daily for uncomplicated disease. 1
• High-dose amoxicillin: 80–90 mg/kg/day divided twice daily for children <2 years, those in daycare, with recent antibiotic use, or in areas with high local resistance. 1
• High-dose amoxicillin-clavulanate: 80–90 mg/kg/day (amoxicillin component) plus 6.4 mg/kg/day clavulanate divided twice daily. 1
• Minimum treatment duration: 10–14 days (longer than adult courses). 1
• Reassess at 72 hours; if no improvement or worsening, switch to high-dose amoxicillin-clavulanate. 1

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Essential Adjunctive Therapies (Add to All Patients)

• Intranasal corticosteroids (mometasone, fluticasone, or budesonide) twice daily significantly reduce mucosal inflammation and accelerate symptom resolution—supported by strong evidence from multiple randomized controlled trials. 1, 2
• Saline nasal irrigation 2–3 times daily provides symptomatic relief and enhances mucus clearance. 1, 2
• Analgesics (acetaminophen or ibuprofen) for pain and fever control. 1, 2

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Watchful Waiting Strategy

• For adults with uncomplicated ABRS and reliable follow-up, initial observation without antibiotics is appropriate. 1, 2
• Start antibiotics only if no improvement by day 7 or if symptoms worsen at any time. 1, 2
• The number needed to treat (NNT) is 10–15 to achieve one additional cure compared with placebo, reflecting the high rate of spontaneous recovery. 1

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Monitoring and Reassessment

Early Reassessment (Days 3–5)

• If no clinical improvement (persistent purulent drainage, unchanged facial pain, or worsening), switch to: 1, 2
  • High-dose amoxicillin-clavulanate 2 g/125 mg twice daily, or
  • Respiratory fluoroquinolone (levofloxacin or moxifloxacin)

Day 7 Reassessment

• Persistent or worsening symptoms require: 1, 2
  1. Confirmation of ABRS diagnosis
  2. Exclusion of complications (orbital cellulitis, meningitis, intracranial abscess)
  3. Imaging only if complications are suspected
  4. Referral to otolaryngology

Expected Timeline of Recovery

• Noticeable improvement within 3–5 days of appropriate therapy. 1
• Complete resolution by 10–14 days or when symptom-free for 7 consecutive days. 1
• Only 30–41% of patients improve by days 3–5; zero improvement at this stage indicates likely treatment failure. 1

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Antibiotics to Avoid

• Macrolides (azithromycin, clarithromycin)—20–25% resistance rates in S. pneumoniae and H. influenzae. The American Academy of Pediatrics explicitly contraindicates azithromycin for ABRS. 1
• Trimethoprim-sulfamethoxazole—≈50% resistance in S. pneumoniae and ≈27% in H. influenzae. 1
• First-generation cephalosporins (cephalexin)—inadequate coverage since ≈50% of H. influenzae strains produce β-lactamase. 1

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Referral to Otolaryngology

Refer immediately for any of the following: 1, 2

• No improvement after 7 days of appropriate second-line antibiotic therapy
• Worsening symptoms at any point during treatment
• Suspected complications: severe headache, visual changes, periorbital swelling/erythema, proptosis, diplopia, altered mental status, cranial nerve deficits
• Recurrent sinusitis (≥3 episodes per year) requiring evaluation for underlying allergic rhinitis, immunodeficiency, or anatomic abnormalities

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Common Pitfalls to Avoid

• Do not obtain routine imaging (X-ray or CT) for uncomplicated ABRS—up to 87% of viral URIs show sinus abnormalities on imaging, leading to unnecessary interventions. 1
• Ensure adequate treatment duration (≥5 days for adults, ≥10 days for children) to prevent relapse. 1
• Gastrointestinal adverse effects with amoxicillin-clavulanate are common: diarrhea in 40–43% of patients; severe diarrhea in 7–8%. 1
• Fluoroquinolones should not be used as first-line therapy in patients without documented β-lactam allergy to limit resistance development. 1, 2