What is the first‑line treatment and dosing for acute bacterial sinusitis in an adult without a penicillin allergy?

First-Line Treatment for Acute Bacterial Sinusitis in Adults Without Penicillin Allergy

Amoxicillin-clavulanate 875 mg/125 mg twice daily for 5–10 days is the preferred first-line antibiotic for adults with acute bacterial sinusitis who have no penicillin allergy. 1, 2

Confirming the Diagnosis Before Prescribing

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

• Persistent symptoms ≥ 10 days with purulent nasal discharge plus either nasal obstruction or facial pain/pressure/fullness 1, 2
• Severe symptoms ≥ 3–4 consecutive days with fever ≥ 39°C (102.2°F), purulent nasal discharge, and facial pain 1, 2
• "Double sickening": initial improvement from a viral upper respiratory infection followed by worsening symptoms within 10 days 1, 2

Do not prescribe antibiotics for symptoms lasting < 10 days unless the severe criteria above are met, because approximately 98–99.5% of acute rhinosinusitis cases are viral and resolve spontaneously within 7–10 days. 1, 3

Standard Dosing and Duration

• Standard regimen: amoxicillin-clavulanate 875 mg/125 mg orally twice daily 1, 2
• Treatment duration: 5–10 days, or continue until the patient is symptom-free for 7 consecutive days (typically 10–14 days total) 1, 2
• Recent evidence supports shorter 5–7 day courses as equally effective with fewer adverse effects compared to traditional 10-day regimens 1, 4

When to Use High-Dose Amoxicillin-Clavulanate

Escalate to high-dose amoxicillin-clavulanate 2 g/125 mg twice daily when the patient has any of these risk factors for resistant organisms:

• Recent antibiotic use within the past 4–6 weeks 1, 2
• Age > 65 years 1
• Moderate-to-severe symptoms 1
• Comorbidities (diabetes, chronic cardiac/hepatic/renal disease) 1
• Immunocompromised state 1
• Daycare exposure (for children or close contacts) 1, 2

Why Amoxicillin-Clavulanate Is Preferred Over Plain Amoxicillin

The clavulanate component is essential because 30–40% of Haemophilus influenzae and 90–100% of Moraxella catarrhalis produce β-lactamase, rendering plain amoxicillin ineffective against these organisms. 1, 5 Amoxicillin-clavulanate provides 90–92% predicted clinical efficacy against the three major sinusitis pathogens: Streptococcus pneumoniae, H. influenzae, and M. catarrhalis. 1, 2

Plain amoxicillin (500 mg twice daily for mild disease or 875 mg twice daily for moderate disease) remains acceptable only for uncomplicated cases in patients who have not received antibiotics in the preceding 4–6 weeks. 1, 2

Essential Adjunctive Therapies (Add to All Patients)

These non-antibiotic therapies significantly improve outcomes and should be prescribed for every patient:

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

Monitoring and Reassessment Protocol

Early Reassessment (Days 3–5)

• If there is no clinical improvement (persistent purulent drainage, unchanged facial pain, or worsening symptoms), switch immediately to a second-line agent 1, 2
• Second-line options include high-dose amoxicillin-clavulanate (if not already used) or a respiratory fluoroquinolone (levofloxacin 500 mg once daily for 10–14 days or moxifloxacin 400 mg once daily for 10 days) 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 1, 2
• Do not wait beyond 3–5 days to change therapy in non-responders, as delayed escalation increases the risk of complications 1

Expected Timeline of Recovery

• Noticeable improvement should occur within 3–5 days of appropriate antibiotic therapy 1
• Complete symptom resolution typically occurs by 10–14 days or when the patient is symptom-free for 7 consecutive days 1
• Only 30–41% of patients show improvement by days 3–5; zero improvement at this point indicates treatment failure 1

Watchful Waiting as an Alternative Strategy

For adults with uncomplicated acute bacterial sinusitis and reliable follow-up, initial observation without antibiotics is appropriate. 1, 2 Start antibiotics only if:

• No improvement by day 7, or
• Symptoms worsen at any time 1

The number needed to treat (NNT) with antibiotics is 10–15 to achieve one additional cure compared with placebo, reflecting the high rate of spontaneous recovery. 1

Common Pitfalls to Avoid

• Do not obtain routine imaging (X-ray or CT) for uncomplicated acute bacterial sinusitis; up to 87% of viral upper respiratory infections show sinus abnormalities on imaging, leading to unnecessary interventions 1
• Gastrointestinal adverse effects are common with amoxicillin-clavulanate: diarrhea occurs in 40–43% of patients, with severe diarrhea in 7–8% 1, 6, 4
• Ensure adequate treatment duration (minimum 5 days for adults) to prevent relapse 1, 2
• Do not use macrolides (azithromycin, clarithromycin) as first-line therapy due to 20–25% resistance rates in S. pneumoniae and H. influenzae 1, 3

When to Refer to Otolaryngology

Immediate referral is indicated for any of the following:

• No improvement after 7 days of appropriate second-line antibiotic therapy 1
• Worsening symptoms at any point 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, 2