Amoxicillin for Sinusitis: Dosing, Duration, Resistance, and Adjunctive Care

Amoxicillin (with or without clavulanate) is first-line for acute bacterial rhinosinusitis (ABRS) when antibiotics are indicated. Most acute sinusitis is viral — antibiotics are not routinely needed.

When Antibiotics Are Indicated (IDSA Guidelines)

• Persistent symptoms ≥10 days without improvement.
• Severe onset: high fever (≥39°C / 102°F) + purulent discharge/facial pain ≥3–4 days.
• Worsening ("double sickening"): Initial improvement then worsening at 5–6 days.

Dosing Regimens

Formulation	Adult Dose	Duration	Notes
Amoxicillin-clavulanate (Augmentin) — Preferred	500 mg/125 mg PO q8h OR 875 mg/125 mg PO q12h	5–7 days (IDSA) / 10 days (traditional)	Clavulanate covers β-lactamase producers (H. influenzae, M. catarrhalis).
Amoxicillin alone	1 g PO q8h	5–10 days	Only if low resistance area, penicillin-allergic (use doxycycline/fluoroquinolone instead).
High-dose Amox-clav	2 g/125 mg PO q12h	5–7 days	For high-risk: age >65, recent antibiotics, immunocompromise, severe disease, daycare exposure.

Pediatric: 45–90 mg/kg/day amoxicillin component divided q12h (high-dose for resistant areas).

Key Principles

• Complete the course even if better — prevents resistance, relapse.
• Shorter courses (5–7 days) are non-inferior to 10 days for uncomplicated ABRS (IDSA 2012, Cochrane).
• Reassess at 3–5 days: No improvement → re-evaluate diagnosis, consider resistant pathogen, imaging, ENT referral.

Adjunctive Symptom Relief

• Saline nasal irrigation (high-volume, isotonic/hypertonic) — Grade A evidence.
• Intranasal corticosteroids (INCS) — reduce inflammation, especially with allergic component.
• Analgesics: NSAIDs or acetaminophen.
• Decongestants (oral/topical): Short-term only (≤3 days topical to avoid rebound).
• Hydration, warm compresses, rest.

Resistance Considerations

• S. pneumoniae: ~30% penicillin-nonsusceptible (high-dose amoxicillin overcomes).
• H. influenzae: ~30% β-lactamase positive (needs clavulanate).
• M. catarrhalis: >90% β-lactamase positive.

Amoxicillin-clavulanate at appropriate dose/duration remains the cornerstone of targeted ABRS therapy.