In otherwise healthy adults with acute bacterial sinusitis, when should antibiotics be prescribed and what is the first‑line regimen, including alternatives for penicillin allergy and adjunctive therapies?

Acute Bacterial Sinusitis: When to Prescribe Antibiotics and First-Line Regimens

When to Prescribe Antibiotics

Antibiotics should be prescribed only when acute bacterial sinusitis is confirmed by at least one of three specific clinical patterns—not simply for purulent nasal discharge or facial pressure alone. 1

Diagnostic Criteria (Must Meet ≥1 of the Following)

• Persistent symptoms ≥10 days without improvement: purulent nasal discharge plus either nasal obstruction or facial pain/pressure/fullness. 123
• Severe symptoms ≥3–4 consecutive days: fever ≥39°C with purulent nasal discharge and facial pain. 123
• "Double sickening": initial improvement from a viral URI followed by worsening symptoms within 10 days. 123

Critical Context: Most Cases Are Viral

• Approximately 98–99.5% of acute rhinosinusitis is viral and resolves spontaneously within 7–10 days without antibiotics. 1
• Do not prescribe antibiotics for symptoms <10 days unless the severe criteria (fever ≥39°C with purulent discharge for ≥3 consecutive days) are present. 13
• The number needed to treat (NNT) with antibiotics is 10–15 patients to achieve one additional cure compared with placebo. 1

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First-Line Antibiotic Regimen

Amoxicillin-clavulanate 875 mg/125 mg orally twice daily for 5–10 days is the preferred first-line regimen for otherwise healthy adults with confirmed acute bacterial sinusitis. 12

Dosing Specifications

• Standard dose: 875 mg/125 mg twice daily for most patients. 1
• High-dose regimen (2 g/125 mg twice daily): use when any of the following risk factors are present—recent antibiotic use (past 4–6 weeks), age >65 years, daycare exposure, moderate-to-severe symptoms, comorbidities (diabetes, chronic cardiac/hepatic/renal disease), or immunocompromised state. 1
• Treatment duration: 5–10 days or until symptom-free for 7 consecutive days (typically 10–14 days total). 14
• Shorter courses (5–7 days) achieve comparable efficacy with fewer adverse effects. 14

Why Amoxicillin-Clavulanate Is Preferred

• Predicted clinical efficacy of 90–92% against the three major pathogens: Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis. 12
• The clavulanate component is essential because 30–40% of H. influenzae and 90–100% of M. catarrhalis produce β-lactamase. 15
• Increasing prevalence of penicillin-resistant S. pneumoniae and β-lactamase-producing organisms makes plain amoxicillin inadequate for most cases. 65

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Alternatives for Penicillin Allergy

Non-Severe (Non-Type I) Penicillin Allergy

Use a second- or third-generation cephalosporin for 10 days; cross-reactivity with penicillin is negligible. 1

• Options: cefuroxime-axetil, cefpodoxime-proxetil, cefdinir, or cefprozil. 16
• These agents provide comparable coverage against sinusitis pathogens. 1

Severe (Type I/Anaphylactic) Penicillin Allergy

Prescribe a respiratory fluoroquinolone with 90–92% predicted efficacy against multidrug-resistant pathogens. 1

• Levofloxacin 500 mg once daily for 10–14 days. 1
• Moxifloxacin 400 mg once daily for 10 days. 1
• Reserve fluoroquinolones for documented severe β-lactam allergy or treatment failure to limit resistance development. 1

Suboptimal Alternative

• Doxycycline 100 mg once daily for 10 days yields only 77–81% predicted efficacy with a 20–25% bacteriologic failure rate due to limited H. influenzae coverage. 1
• Use only when fluoroquinolones and cephalosporins are contraindicated. 1

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Antibiotics to Avoid

• Macrolides (azithromycin, clarithromycin): resistance rates 20–25% for both S. pneumoniae and H. influenzae; explicitly contraindicated. 12
• Trimethoprim-sulfamethoxazole: 50% resistance in S. pneumoniae and 27% in H. influenzae. 1
• First-generation cephalosporins (cephalexin): inadequate coverage because ~50% of H. influenzae strains produce β-lactamase. 1

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Essential Adjunctive Therapies (Add to All Patients)

Intranasal corticosteroids significantly reduce mucosal inflammation and accelerate symptom resolution; supported by strong evidence from multiple randomized controlled trials. 12

• Intranasal corticosteroids (mometasone, fluticasone, or budesonide) twice daily. 12
• Saline nasal irrigation 2–3 times daily for symptomatic relief and mucus clearance. 12
• Analgesics (acetaminophen or ibuprofen) for pain and fever control. 12
• Decongestants (oral or topical); limit topical use to ≤3 days to avoid rebound congestion. 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 promptly to high-dose amoxicillin-clavulanate or a respiratory fluoroquinolone. 12
• Only 30–41% of patients show improvement by days 3–5; zero improvement at this point indicates likely treatment failure. 1

Day 7 Reassessment

• Persistent or worsening symptoms warrant confirmation of diagnosis, exclusion of complications (orbital cellulitis, meningitis, intracranial abscess), and consideration of imaging or ENT referral. 12
• By day 7, approximately 73–85% of patients show clinical improvement even with placebo. 1

Expected Timeline

• Most patients experience noticeable improvement within 3–5 days of appropriate antibiotic therapy. 12
• Complete resolution typically occurs by 10–14 days or when symptom-free for 7 consecutive days. 12

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Watchful Waiting Option

For uncomplicated acute bacterial sinusitis with reliable follow-up, initial observation without antibiotics is appropriate; initiate antibiotics only if no improvement by day 7 or if symptoms worsen at any time. 1

• This approach reduces unnecessary antibiotic exposure while maintaining safety. 1
• The NNT of 10–15 reflects the high rate of spontaneous recovery. 1

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Referral to Otolaryngology

Refer immediately if any of the following occur:

• No improvement after 7 days of appropriate second-line antibiotic therapy. 1
• Worsening symptoms at any point (increasing facial pain, fever, purulent drainage). 1
• Suspected complications: severe headache, visual changes, periorbital swelling/erythema, proptosis, diplopia, altered mental status, or cranial nerve deficits. 1
• Recurrent sinusitis (≥3 episodes per year) requiring evaluation for underlying allergic rhinitis, immunodeficiency, or anatomic abnormalities. 1

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Critical Pitfalls to Avoid

• Do not prescribe antibiotics based solely on purulent nasal discharge; this reflects neutrophilic inflammation common to viral disease. 1
• Do not obtain routine imaging (X-ray or CT) for uncomplicated acute bacterial sinusitis; up to 87% of viral URIs show sinus abnormalities on imaging. 1
• Ensure minimum treatment duration (≥5 days for adults) to prevent relapse. 14
• Gastrointestinal adverse effects with amoxicillin-clavulanate are common: diarrhea in 40–43% of patients; severe diarrhea in 7–8%. 1
• Do not use fluoroquinolones as first-line therapy in patients without documented β-lactam allergy to avoid promoting resistance. 1