Cephalexin Should NOT Be Used for Sinus Infections
Cephalexin is inappropriate for treating acute bacterial sinusitis due to inadequate coverage against Haemophilus influenzae, one of the three most common causative pathogens. 1
Why Cephalexin Fails in Sinusitis
Critical Coverage Gap
- First-generation cephalosporins like cephalexin and cefadroxil have poor coverage for H. influenzae and are therefore explicitly deemed inappropriate for sinusitis treatment 1
- The three primary pathogens in acute bacterial sinusitis are Streptococcus pneumoniae, H. influenzae, and Moraxella catarrhalis 1
- Nearly 50% of H. influenzae strains produce β-lactamase, rendering them resistant to first-generation cephalosporins 1
- 90-100% of M. catarrhalis strains are β-lactamase producing 1
FDA Labeling Does Not Support Use
- The FDA-approved indications for cephalexin include respiratory tract infections caused by S. pneumoniae and S. pyogenes, but notably exclude sinusitis 2
- The label specifically mentions otitis media (which shares similar pathogens with sinusitis) but does not list sinusitis as an approved indication 2
What You Should Use Instead
First-Line Options
- Amoxicillin 500 mg twice daily (mild disease) or 875 mg twice daily (moderate disease) for 10-14 days 3
- High-dose amoxicillin-clavulanate (875 mg/125 mg twice daily) provides enhanced coverage against β-lactamase-producing organisms 3, 4
For Penicillin-Allergic Patients
- Second-generation cephalosporins: cefuroxime axetil, cefprozil 1, 3
- Third-generation cephalosporins: cefpodoxime proxetil, cefdinir (NOT cefixime or ceftibuten, which have poor S. pneumoniae coverage) 1
- Respiratory fluoroquinolones: levofloxacin or moxifloxacin (reserve for treatment failures or severe disease) 1, 3
Historical Context: Why This Matters
- A 1985 study showed cephalexin had 83% clinical success in maxillary sinusitis, but this predates the current understanding of β-lactamase-producing organisms 5
- Modern surveillance demonstrates that 42% of H. influenzae strains produce β-lactamase, making first-generation cephalosporins obsolete for this indication 6
- Comparative studies show second-generation cephalosporins (like cefuroxime axetil) achieve 95% bacteriologic cure versus 71% for older agents like cefaclor 6
Critical Pitfall to Avoid
Do not confuse cephalexin with newer-generation cephalosporins. While cefdinir, cefpodoxime, and cefuroxime are appropriate alternatives for penicillin-allergic patients, cephalexin lacks the necessary spectrum of activity and should never be prescribed for sinusitis 1, 3, 7.