First-Line Antibiotic for Sinusitis
Amoxicillin-clavulanate 875 mg/125 mg twice daily for 5-10 days is the preferred first-line antibiotic for acute bacterial sinusitis in adults. 1, 2
Confirming Bacterial Sinusitis Before Prescribing
Before prescribing any antibiotic, confirm the diagnosis meets one of three criteria for acute bacterial rhinosinusitis (ABRS) 1, 2:
- Persistent symptoms ≥10 days without improvement (nasal drainage, congestion, facial pressure/pain) 1, 2
- Severe symptoms ≥3-4 consecutive days (fever ≥39°C with purulent nasal discharge) 1, 2, 3
- "Double sickening" - worsening symptoms after initial improvement from a viral upper respiratory infection 1, 2
Critical caveat: 98-99.5% of acute rhinosinusitis is viral and resolves spontaneously within 7-10 days without antibiotics 2. Do not prescribe antibiotics for symptoms lasting <10 days unless severe features are present 1, 2.
First-Line Treatment Algorithm
For Adults Without Penicillin Allergy
Amoxicillin-clavulanate 875 mg/125 mg twice daily for 5-10 days is the preferred first-line agent 1, 2. This provides 90-92% predicted clinical efficacy against the major pathogens: Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis 2, 4.
High-dose amoxicillin-clavulanate (2 g amoxicillin/125 mg clavulanate twice daily) should be used for patients with 1, 2:
- Recent antibiotic use within the past 4-6 weeks 2
- Age >65 years 2
- Moderate-to-severe symptoms 2
- Comorbid conditions or immunocompromised state 2
Alternative: Plain amoxicillin 500 mg twice daily (mild disease) or 875 mg twice daily (moderate disease) is acceptable for uncomplicated cases without recent antibiotic exposure 2, though the IDSA guideline gives amoxicillin-clavulanate a strong recommendation due to increasing prevalence of β-lactamase-producing organisms 1.
For Penicillin-Allergic Patients (Non-Severe Allergy)
Second- or third-generation cephalosporins are preferred 1, 2:
- Cefuroxime-axetil (second-generation) 2
- Cefpodoxime-proxetil (third-generation) 2
- Cefdinir (third-generation) 2
The risk of cross-reactivity with cephalosporins in penicillin-allergic patients is negligible 2, 5.
For Severe Penicillin Allergy or Cephalosporin Allergy
Respiratory fluoroquinolones are the treatment of choice 2, 5:
These provide 90-92% predicted clinical efficacy with excellent coverage against multi-drug resistant S. pneumoniae 2, 5, 4.
Doxycycline 100 mg once daily for 10 days is an acceptable alternative but has a predicted bacteriologic failure rate of 20-25% and limited activity against H. influenzae 2.
For Children
Amoxicillin 45 mg/kg/day in 2 divided doses for standard therapy 2
High-dose amoxicillin 80-90 mg/kg/day in 2 divided doses for 2:
- Age <2 years 2
- Daycare attendance 2
- Recent antibiotic use 2
- Areas with high prevalence of resistant S. pneumoniae 2
Amoxicillin-clavulanate 80-90 mg/kg/day of amoxicillin component with 6.4 mg/kg/day clavulanate in 2 divided doses for children with risk factors 2
Treatment duration for children is 10-14 days 1, 2, which is longer than the 5-7 days recommended for adults 1.
Treatment Duration
Adults: 5-7 days is the recommended duration for uncomplicated ABRS 1. Recent evidence supports shorter 5-7 day courses with comparable efficacy to 10-day regimens and fewer adverse effects 2. Most guidelines recommend treatment until symptom-free for 7 days, typically resulting in 10-14 days total 2.
Children: 10-14 days is still recommended despite adult data supporting shorter courses 1, 2.
When to Reassess and Switch Antibiotics
- If no improvement or worsening symptoms, switch to second-line therapy 1, 2
- Switch to high-dose amoxicillin-clavulanate (if not already on it) or a respiratory fluoroquinolone 2
Reassess at 7 days 2:
- If symptoms persist, reconfirm diagnosis and consider complications 2
- Switch to broader-spectrum antibiotics if bacterial sinusitis is confirmed 2
For children, reassess at 72 hours and switch to high-dose amoxicillin-clavulanate if worsening or no improvement 2.
Essential Adjunctive Therapies
Intranasal corticosteroids (mometasone, fluticasone, or budesonide twice daily) are strongly recommended as adjunctive therapy in all patients to reduce mucosal inflammation and improve symptom resolution 1, 2.
Saline nasal irrigation provides symptomatic relief and removes mucus 1, 2.
Analgesics (acetaminophen or ibuprofen) for pain and fever 2.
Short-term oral corticosteroids may be considered for patients with marked mucosal edema or who fail to respond to initial treatment 1, 2.
Watchful Waiting Option
For adults with uncomplicated ABRS, watchful waiting without immediate antibiotics is an appropriate initial strategy when reliable follow-up can be assured 2. Antibiotics should be started only if no improvement occurs by 7 days or symptoms worsen at any time 2. This approach is supported by evidence showing that 73% of bacterial sinusitis improves spontaneously by 7-12 days without antibiotics 2.
Critical Pitfalls to Avoid
Do not use azithromycin or other macrolides as first-line therapy due to resistance rates of 20-25% for both S. pneumoniae and H. influenzae 1, 2, 6.
Do not use trimethoprim-sulfamethoxazole due to 50% resistance for S. pneumoniae and 27% resistance for H. influenzae 2.
Do not use first-generation cephalosporins (cephalexin, cefadroxil) due to inadequate coverage against H. influenzae 2.
Reserve fluoroquinolones for second-line therapy or for patients with documented severe β-lactam allergies to prevent resistance development 1, 2, 4.
Do not prescribe antibiotics for symptoms <10 days unless severe symptoms are present 1, 2.
Ensure adequate treatment duration (minimum 5 days for adults, 10 days for children) to prevent relapse 1, 2.
When to Refer to a Specialist
Refer to otolaryngology, infectious disease, or allergy specialist for 1, 2: