Amoxicillin Dosing for Acute Bacterial Sinusitis
For adults with acute bacterial sinusitis, use amoxicillin 875 mg twice daily OR 500 mg three times daily for 5-7 days after symptom resolution (minimum 10 days total); for children ≥3 months and <40 kg, use 45 mg/kg/day divided every 12 hours (or 40 mg/kg/day divided every 8 hours) for the same duration. 1
Adults (≥40 kg)
Standard dosing:
- 875 mg every 12 hours (preferred for convenience)
- OR 500 mg every 8 hours
- Duration: Continue for 48-72 hours after becoming asymptomatic, with minimum 10 days total treatment 1
The 2025 AAO-HNS guideline notably changed first-line therapy from amoxicillin alone to amoxicillin with or without clavulanate 2. However, the most recent high-quality evidence from a 2026 JAMA study of 521,244 patients found no difference in treatment failure between amoxicillin-clavulanate and amoxicillin alone (3.0% vs 3.1%; RR 0.96), while amoxicillin-clavulanate carried higher risks of yeast infections (1.1% vs 0.8%) and C. difficile infections (0.04% vs 0.02%) 3. This suggests plain amoxicillin is preferred as first-line unless risk factors for resistant organisms exist.
When to use amoxicillin-clavulanate instead:
- Recent antibiotic use (within 30 days)
- Daycare attendance
- Age >65 years
- Immunocompromised state
- Failed initial amoxicillin therapy after 72 hours
Pediatric Patients
Children ≥3 months and <40 kg:
- 45 mg/kg/day divided every 12 hours (preferred)
- OR 40 mg/kg/day divided every 8 hours
- Maximum dose: Do not exceed adult dosing 1
Infants <3 months:
- Maximum 30 mg/kg/day divided every 12 hours (due to immature renal function) 1
- Duration: Minimum 10 days to prevent complications 4
The 2014 AAP guideline specifies three clinical presentations warranting antibiotics in children: persistent symptoms >10 days, severe onset (fever ≥102.2°F with purulent discharge for ≥3 days), or worsening symptoms after initial improvement 4.
Renal Impairment Adjustments
For adults and children >40 kg with severe renal dysfunction:
| GFR | Dosing Regimen |
|---|---|
| 10-30 mL/min | 500 mg or 250 mg every 12 hours |
| <10 mL/min | 500 mg or 250 mg every 24 hours |
| Hemodialysis | 500 mg or 250 mg every 24 hours + additional dose during and after dialysis |
Critical caveat: Patients with GFR <30 mL/min should NOT receive the 875 mg dose 1
Penicillin Allergy Alternatives
For true penicillin allergy (Type I hypersensitivity):
- Cefdinir, cefuroxime, or cefpodoxime (use with caution; 10% cross-reactivity risk)
- Avoid azithromycin and trimethoprim-sulfamethoxazole due to high resistance rates in S. pneumoniae and H. influenzae 4
For severe/anaphylactic reactions:
- Respiratory fluoroquinolones (adults only)
- Consider infectious disease consultation
Administration Pearls
- Take at the start of meals to minimize GI intolerance 1
- Ensure adequate hydration
- Complete full course even if symptoms resolve early
Common Pitfalls to Avoid
Don't use 875 mg dose in severe renal impairment (GFR <30 mL/min) - this is explicitly contraindicated 1
Don't automatically escalate to amoxicillin-clavulanate - the 2026 JAMA study demonstrates plain amoxicillin is equally effective with fewer adverse events in uncomplicated cases 3
Don't underdose children - the FDA label clearly specifies 45 mg/kg/day for ear/nose/throat infections, not the lower 25 mg/kg/day dose 1
Don't use azithromycin or TMP-SMX for penicillin allergy - resistance patterns make these poor choices 4
Don't treat for <10 days - inadequate duration risks treatment failure and complications 1