What is the recommended dose of amoxicillin (amoxicillin) for treating acute bacterial sinusitis in adults and children?

Amoxicillin Dosing for Acute Bacterial Sinusitis

For adults with acute bacterial sinusitis, use amoxicillin-clavulanate 875 mg/125 mg twice daily for 5-10 days as first-line therapy, or high-dose amoxicillin-clavulanate 2 g/125 mg twice daily for patients with recent antibiotic use, age >65 years, or severe disease. 1, 2 For children, use standard-dose amoxicillin 45 mg/kg/day divided twice daily for uncomplicated cases, or high-dose amoxicillin-clavulanate 80-90 mg/kg/day (of amoxicillin component) with 6.4 mg/kg/day clavulanate divided twice daily for high-risk children. 1, 3

Adult Dosing Recommendations

Standard First-Line Therapy

• Amoxicillin-clavulanate 875 mg/125 mg twice daily for 5-10 days is the preferred first-line antibiotic for most adults with acute bacterial sinusitis. 1, 2
• Plain amoxicillin 500 mg twice daily (mild disease) or 875 mg twice daily (moderate disease) remains acceptable for uncomplicated cases without recent antibiotic exposure. 2
• The IDSA guidelines recommend amoxicillin-clavulanate over plain amoxicillin due to increasing prevalence of β-lactamase-producing organisms (Haemophilus influenzae and Moraxella catarrhalis). 1

High-Dose Therapy Indications

Use high-dose amoxicillin-clavulanate 2 g/125 mg twice daily when patients have: 1, 2

• Recent antibiotic use within the past 4-6 weeks
• Age >65 years
• Moderate-to-severe symptoms (fever ≥39°C with purulent discharge)
• Comorbid conditions (diabetes, COPD, immunosuppression)
• Geographic areas with high prevalence (>10%) of penicillin-resistant S. pneumoniae

Treatment Duration

• Adults: 5-7 days for uncomplicated cases (weak recommendation, low-moderate evidence). 1
• Alternative approach: Continue treatment until symptom-free for 7 days, typically resulting in 10-14 days total. 2
• Shorter 5-7 day courses have comparable efficacy to 10-day regimens with fewer adverse effects. 4, 5

Pediatric Dosing Recommendations

Standard-Dose Amoxicillin

For children ≥2 years without risk factors: 3

• Amoxicillin 45 mg/kg/day divided into 2 doses
• Example: For a 16 kg child, give 360 mg twice daily (720 mg/day total)
• This remains first-line based on effectiveness against S. pneumoniae, safety profile, acceptable taste, and low cost. 3

High-Dose Amoxicillin-Clavulanate

Use 80-90 mg/kg/day (of amoxicillin component) with 6.4 mg/kg/day clavulanate divided twice daily for children with: 1, 3, 6

• Age <2 years
• Daycare attendance
• Antibiotic use within past 4-6 weeks
• Geographic areas with high prevalence (>10%) of resistant S. pneumoniae
• Treatment failure after 72 hours of standard-dose amoxicillin

Pediatric Treatment Duration

• Children: 10-14 days minimum, or continue for 7 days after becoming symptom-free. 1, 3
• This longer duration compared to adults is necessary despite adult data supporting shorter courses. 1

Critical Reassessment Timepoints

Adults

• Reassess at 3-5 days: If no improvement, switch to high-dose amoxicillin-clavulanate or respiratory fluoroquinolone (levofloxacin 500 mg once daily). 2
• Reassess at 7 days: If symptoms persist or worsen, reconfirm diagnosis and consider complications or alternative diagnoses. 2

Children

• Reassess at 72 hours: If symptoms worsen or fail to improve, switch to high-dose amoxicillin-clavulanate (90 mg/kg/day of amoxicillin component). 3
• Treatment failure at 72 hours suggests β-lactamase-producing organisms requiring clavulanate coverage. 3

Alternative for Vomiting or Non-Compliance (Pediatrics)

• Ceftriaxone 50 mg/kg IM or IV as a single dose for children who cannot tolerate oral medications. 3
• After clinical improvement, switch to oral amoxicillin to complete the 10-14 day course. 3

Adjunctive Therapies to Enhance Outcomes

Add these to antibiotic therapy for all patients: 1, 2

• Intranasal corticosteroids (mometasone, fluticasone, or budesonide twice daily) reduce mucosal inflammation
• Saline nasal irrigation provides symptomatic relief
• Analgesics (acetaminophen or ibuprofen) for pain and fever

Critical Pitfalls to Avoid

Diagnostic Errors

• Do not prescribe antibiotics for symptoms <10 days unless severe features present (fever ≥39°C with purulent discharge for ≥3 consecutive days). 1, 2
• 98-99.5% of acute rhinosinusitis is viral and resolves spontaneously within 7-10 days without antibiotics. 2

Inappropriate Antibiotic Selection

• Avoid azithromycin and other macrolides due to 20-25% resistance rates for both S. pneumoniae and H. influenzae. 1, 2
• Avoid trimethoprim-sulfamethoxazole due to 50% resistance for S. pneumoniae and 27% for H. influenzae. 2
• Avoid first-generation cephalosporins (cephalexin) due to inadequate coverage against H. influenzae. 2

Treatment Duration Errors

• Inadequate treatment duration leads to relapse—ensure minimum 5 days for adults and 10 days for children. 1, 2, 3
• Waiting beyond 7 days (adults) or 72 hours (children) to change therapy in non-responders delays effective treatment. 2, 3

Evidence for High-Dose vs Standard-Dose

The evidence for high-dose amoxicillin-clavulanate superiority is mixed. One 2018 study found that immediate-release high-dose (1750 mg amoxicillin twice daily) provided 18% greater improvement at day 3 compared to standard-dose (52.4% vs 34.4%, P=0.04), but with increased severe diarrhea (15.8% vs 4.8%). 5 However, a 2021 study found no benefit of high-dose over standard-dose at day 3 (36.4% vs 44.3%, P=0.35). 7 Despite mixed efficacy data, high-dose therapy demonstrates superior eradication of resistant S. pneumoniae from the nasopharynx. 8

Given this conflicting evidence, reserve high-dose therapy for patients with specific risk factors rather than using it routinely. 1, 2