What is the recommended dose, dosing frequency, and duration of first‑line amoxicillin for uncomplicated acute bacterial rhinosinusitis in adults and children?

Amoxicillin Dosing for First-Line Treatment of Acute Bacterial Rhinosinusitis

Adults

For uncomplicated acute bacterial rhinosinusitis in adults, amoxicillin-clavulanate 875 mg/125 mg twice daily for 5–7 days is the preferred first-line regimen, providing 90–92% predicted clinical efficacy against the major pathogens. 1, 2

Standard Dosing

• Dose: 875 mg/125 mg orally twice daily 1, 2
• Duration: 5–7 days (or until 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, 2

High-Dose Regimen (for Risk Factors)

• Dose: 2 g amoxicillin/125 mg clavulanate twice daily 1, 2
• Indications for high-dose: Recent antibiotic use (past 4–6 weeks), age >65 years, daycare exposure, moderate-to-severe symptoms, comorbidities, or immunocompromised state 1, 2
• High-dose formulation achieves 90–92% predicted clinical efficacy against drug-resistant Streptococcus pneumoniae 1

Plain Amoxicillin (Less Preferred)

• Dose: 500 mg twice daily (mild disease) or 875 mg twice daily (moderate disease) 1, 3
• Duration: 5–10 days 1
• Plain amoxicillin may be used only for mild disease in patients without recent antibiotic exposure (past 4–6 weeks), but amoxicillin-clavulanate is generally preferred due to β-lactamase-producing organisms 1

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Children (≥3 Months and <40 kg)

For children with acute bacterial rhinosinusitis, high-dose amoxicillin-clavulanate 90 mg/kg/day (amoxicillin component) with 6.4 mg/kg/day clavulanate divided twice daily for 10–14 days is strongly recommended as first-line therapy. 1, 4

Standard-Dose Regimen

• Dose: 45 mg/kg/day (amoxicillin component) divided twice daily 1, 4, 5
• Duration: 10–14 days (or continue for 7 days after symptom-free) 1, 4
• Appropriate for uncomplicated disease without risk factors 1, 4

High-Dose Regimen (Preferred for Most Children)

• Dose: 80–90 mg/kg/day (amoxicillin component) with 6.4 mg/kg/day clavulanate divided twice daily 1, 4, 5
• Maximum: 4,000 mg/day amoxicillin 2, 4
• Duration: 10–14 days 1, 4
• Indications: Age <2 years, daycare attendance, recent antibiotic use (past 4–6 weeks), incomplete *Haemophilus influenzae* type b vaccination, areas with high prevalence of penicillin-resistant *S. pneumoniae* (>10%), moderate-to-severe illness, or concurrent purulent otitis media 1, 2, 4
• The 14:1 ratio formulation (90/6.4 mg/kg/day) causes less diarrhea than other amoxicillin-clavulanate preparations while maintaining efficacy 2, 4

Plain Amoxicillin (Alternative)

• Dose: 45 mg/kg/day divided twice daily (standard) or 80–90 mg/kg/day divided twice daily (high-dose) 1, 4, 5
• Duration: 10–14 days 1, 4
• Plain amoxicillin may be considered for uncomplicated cases without risk factors, but amoxicillin-clavulanate is preferred due to β-lactamase-producing organisms 1, 5

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Infants <3 Months

• Dose: Maximum 30 mg/kg/day divided every 12 hours 3
• Duration: Minimum 48–72 hours beyond symptom resolution 3
• Due to incompletely developed renal function, the upper dose limit is lower in this age group 3

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Key Monitoring & Reassessment

Adults

• Reassess at 3–5 days: If no improvement, switch to high-dose amoxicillin-clavulanate or a respiratory fluoroquinolone 1, 2, 6
• Reassess at 7 days: Persistent or worsening symptoms warrant diagnostic reconsideration, exclusion of complications, and possible imaging or ENT referral 1, 2, 6

Children

• Reassess at 72 hours: If no improvement or worsening, switch to high-dose amoxicillin-clavulanate 1, 4
• Clinical improvement should be evident within 48–72 hours 2, 4

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Critical Pitfalls to Avoid

• Do not prescribe antibiotics for symptoms <10 days unless severe features are present (fever ≥39°C with purulent discharge for ≥3 consecutive days), as 98–99.5% of acute rhinosinusitis is viral 1, 2, 6
• Ensure minimum treatment duration: ≥5 days for adults and ≥10 days for children to prevent relapse 1, 2, 4
• Gastrointestinal adverse effects are common with amoxicillin-clavulanate (diarrhea in 40–43% of patients; severe diarrhea in 7–8%) 2, 7, 8
• Reassess early (3–5 days for adults, 72 hours for children): Delaying changes in non-responders can allow complications to develop 1, 2, 4

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Adjunctive Therapies (Add to All Patients)

• Intranasal corticosteroids (mometasone, fluticasone, or budesonide) twice daily reduce mucosal inflammation and accelerate symptom resolution; supported by strong evidence from multiple randomized controlled trials 1, 2, 6
• Saline nasal irrigation 2–3 times daily provides symptomatic relief and aids mucus clearance 1, 2, 6
• Analgesics (acetaminophen or ibuprofen) for pain and fever control 1, 2, 6