Cephalexin for Acute Bacterial Sinusitis
Cephalexin is NOT recommended as first-line therapy for acute bacterial sinusitis because it lacks adequate coverage against the most common pathogens, particularly β-lactamase-producing Haemophilus influenzae and Moraxella catarrhalis. 1, 2
Why Cephalexin is Inappropriate
- First-generation cephalosporins like cephalexin should be discontinued immediately and replaced with an appropriate antibiotic due to inadequate coverage for common sinusitis pathogens 2
- Nearly 50% of H. influenzae and 90-100% of M. catarrhalis produce β-lactamase, rendering first-generation cephalosporins ineffective 2
- The three primary bacterial pathogens in acute sinusitis are Streptococcus pneumoniae, H. influenzae, and M. catarrhalis 2
Recommended First-Line Treatment Instead
Amoxicillin-clavulanate 875 mg/125 mg twice daily is the preferred first-line antibiotic for acute bacterial sinusitis in adults. 1, 2
Alternative First-Line Options:
- Plain amoxicillin 500 mg twice daily (for mild disease without recent antibiotic exposure) or 875 mg twice daily (for moderate disease) remains acceptable for uncomplicated cases 1
- For penicillin-allergic patients: Second-generation cephalosporins (cefuroxime-axetil 500 mg twice daily) or third-generation cephalosporins (cefpodoxime-proxetil, cefdinir, cefprozil) provide significantly enhanced activity against β-lactamase-producing organisms 1, 2
Treatment Duration
- Standard duration is 10-14 days, or until symptom-free for 7 days 1, 2
- Shorter 5-7 day courses have comparable efficacy with fewer side effects for uncomplicated cases 1, 3
- The evidence strongly supports reduction to 5-day courses for uncomplicated acute maxillary sinusitis in adults 3, 4
When to Reserve Antibiotics
Antibiotics should be reserved for patients meeting specific clinical criteria: 5
- Persistent symptoms for more than 10 days without clinical improvement
- Severe symptoms: fever >39°C, purulent nasal discharge, or facial pain lasting ≥3 consecutive days
- "Double sickening": worsening symptoms after initial improvement for >3 days
Second-Line Treatment for Failure
- If no improvement after 3-5 days, switch to a different antibiotic class 1, 2
- Respiratory fluoroquinolones (levofloxacin 500-750 mg once daily or moxifloxacin) are reserved for treatment failures, complicated sinusitis, or multi-drug resistant organisms 1
Critical Pitfalls to Avoid
- Never use azithromycin or clarithromycin due to 20-25% resistance rates 1, 2
- Avoid fluoroquinolones as routine first-line therapy to prevent resistance development 1
- Ensure complete antibiotic course even after symptom improvement to prevent relapse 2
- Reassess at 3-5 days if no improvement to avoid treatment failure 1
Historical Context on Cephalexin
While one older study from 1985 showed cephalexin 1 g/day in four divided doses for 10 days achieved 83% satisfactory clinical results 6, this predates the current understanding of β-lactamase-producing organisms and resistance patterns. Current guidelines explicitly exclude first-generation cephalosporins from recommended therapy. 1, 2