What is the recommended medication regimen for an otherwise healthy adult with acute bacterial sinusitis, including first‑line therapy and alternatives for penicillin allergy or recent antibiotic use?

Medication Regimen for Adult Acute Bacterial Sinusitis

Amoxicillin-clavulanate 875 mg/125 mg twice daily for 5–10 days is the first-line antibiotic for otherwise healthy adults with acute bacterial sinusitis. 1, 2

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Confirm the Diagnosis Before Prescribing

Before initiating antibiotics, verify that the patient meets at least one of three diagnostic criteria for bacterial (not viral) sinusitis 1, 3:

• Persistent symptoms ≥10 days without improvement (purulent nasal discharge plus nasal obstruction or facial pain/pressure) 1, 3
• Severe symptoms ≥3–4 consecutive days with fever ≥39°C, purulent nasal discharge, and facial pain 1, 3
• "Double sickening": initial improvement from a viral URI followed by worsening within 10 days 1, 3

Do not prescribe antibiotics for symptoms <10 days unless severe features are present, because 98–99.5% of acute rhinosinusitis is viral and resolves spontaneously within 7–10 days. 1, 3

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First-Line Antibiotic Therapy

Standard Regimen

• 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
• Predicted clinical efficacy: 90–92% against Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis 1
• The clavulanate component is essential because 30–40% of H. influenzae and 90–100% of M. catarrhalis produce β-lactamase, rendering plain amoxicillin ineffective 1, 4

High-Dose Regimen (When Indicated)

Use high-dose amoxicillin-clavulanate 2 g/125 mg twice daily if the patient has any of the following risk factors 1, 3:

• Recent antibiotic use within the past 4–6 weeks 1
• Age >65 years 1
• Daycare exposure (patient or household contact) 1, 3
• Moderate-to-severe symptoms 1
• Comorbidities (diabetes, chronic cardiac/hepatic/renal disease) 1
• Immunocompromised state 1

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Treatment Duration

• Standard course: 5–10 days, or continue until symptom-free for 7 consecutive days (typically 10–14 days total) 1, 2
• Shorter 5–7 day courses provide comparable efficacy with fewer adverse effects and are increasingly recommended 1, 5, 6
• Ensure a minimum of 5 days to prevent relapse 1

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Alternatives for Penicillin Allergy

Non-Severe (Non-Type I) Penicillin Allergy

For patients with a mild rash or non-anaphylactic reaction, use a second- or third-generation cephalosporin for 10 days 1, 2:

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

Cross-reactivity with penicillin is negligible for these agents. 1

Severe (Type I/Anaphylactic) Penicillin Allergy

For patients with documented anaphylaxis, urticaria, or angioedema to penicillin, use a respiratory fluoroquinolone 1, 2:

• Levofloxacin 500 mg once daily for 10–14 days 1, 2
• Moxifloxacin 400 mg once daily for 10 days 1, 2

Both provide 90–92% predicted efficacy against multidrug-resistant S. pneumoniae and β-lactamase-producing organisms. 1

Suboptimal Alternative

Doxycycline 100 mg once daily for 10 days is acceptable but suboptimal, with only 77–81% predicted efficacy and a 20–25% bacteriologic failure rate due to limited activity against H. influenzae. 1 Reserve this for patients who cannot tolerate cephalosporins or fluoroquinolones.

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Antibiotics to Avoid

• Macrolides (azithromycin, clarithromycin): 20–25% resistance rates in S. pneumoniae and H. influenzae make them unsuitable 1, 2
• Trimethoprim-sulfamethoxazole: 50% resistance in S. pneumoniae and 27% in H. influenzae 1
• First-generation cephalosporins (cephalexin): inadequate coverage against H. influenzae because ~50% of strains produce β-lactamase 1

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Essential Adjunctive Therapies (Add to All Patients)

Intranasal Corticosteroids (Strong Evidence)

• Mometasone, fluticasone, or budesonide twice daily significantly reduce mucosal inflammation and accelerate symptom resolution 1, 2
• Supported by strong evidence from multiple randomized controlled trials 1

Saline Nasal Irrigation

• 2–3 times daily for symptomatic relief and mucus clearance 1, 2

Analgesics

• Acetaminophen or ibuprofen for pain and fever control 1, 2

Decongestants

• Oral or topical decongestants may be used; limit topical agents to ≤3 days to avoid rebound congestion 1

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Monitoring and Reassessment

Reassess at 3–5 Days

• If no clinical improvement (persistent purulent drainage, unchanged facial pain, or worsening), switch immediately to 1, 2:
  • High-dose amoxicillin-clavulanate 2 g/125 mg twice daily, or
  • Respiratory fluoroquinolone (levofloxacin 500 mg daily or moxifloxacin 400 mg daily)

Reassess at 7 Days

• If symptoms persist or worsen, reconfirm the diagnosis, exclude complications (orbital cellulitis, meningitis, intracranial abscess), and consider imaging or ENT referral 1, 2
• Only 30–41% of patients show improvement by days 3–5; zero improvement at this point indicates treatment failure 1

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Watchful Waiting Option

For uncomplicated cases with reliable follow-up, initial observation without antibiotics is appropriate 1, 2:

• Initiate antibiotics only if no improvement by day 7 or if symptoms worsen at any time 1
• The number needed to treat (NNT) with antibiotics is 10–15 to achieve one additional cure, reflecting the high rate of spontaneous recovery 1

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When to Refer to Otolaryngology

Refer immediately if any of the following occur 1, 2:

• No improvement after 7 days of appropriate second-line antibiotic therapy 1
• Worsening symptoms at any time during treatment 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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Common Pitfalls to Avoid

• Do not use plain amoxicillin as first-line therapy given the high prevalence of β-lactamase-producing organisms 1, 4
• Do not prescribe antibiotics for symptoms <10 days unless severe features (fever ≥39°C with purulent discharge for ≥3 consecutive days) are present 1, 3
• Do not use fluoroquinolones as first-line therapy in patients without documented β-lactam allergy to prevent resistance development 1
• Gastrointestinal adverse effects with amoxicillin-clavulanate are common: diarrhea in 40–43% of patients, severe diarrhea in 7–8% 1, 7
• Ensure adequate treatment duration (minimum 5 days for adults) to prevent relapse 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, leading to unnecessary interventions 1