Is cephalexin (cephalexin) effective for treating sinus infections?

Cephalexin for Sinus Infection

Cephalexin is NOT recommended for treating sinus infections because it has poor coverage against Haemophilus influenzae, one of the three most common bacterial pathogens in acute bacterial sinusitis, making it an inappropriate choice for empiric therapy. 1

Why Cephalexin Fails as First-Line Therapy

First-generation cephalosporins like cephalexin and cefadroxil have a critical coverage gap that disqualifies them from use in sinusitis:

• Inadequate H. influenzae coverage: These agents cannot reliably cover H. influenzae, which accounts for a substantial proportion of acute bacterial sinusitis cases alongside Streptococcus pneumoniae and Moraxella catarrhalis 1
• Beta-lactamase resistance problem: Nearly 50% of H. influenzae and 90-100% of M. catarrhalis produce beta-lactamase enzymes, rendering first-generation cephalosporins ineffective 1
• FDA labeling limitation: The FDA-approved indications for cephalexin include respiratory tract infections caused only by S. pneumoniae and S. pyogenes—sinusitis is not listed as an approved indication 2

What You Should Prescribe Instead

First-Line Treatment (Access Antibiotics)

Amoxicillin-clavulanate is the preferred first-line antibiotic for acute bacterial sinusitis:

• Adults: 875 mg/125 mg twice daily for 7-10 days 3, 4
• Children: 80-90 mg/kg/day of amoxicillin component with 6.4 mg/kg/day clavulanate in 2 divided doses (maximum 2 g per dose) 1
• Rationale: Provides coverage against all three major pathogens including beta-lactamase-producing organisms 1, 4

Plain amoxicillin (without clavulanate) remains acceptable only for uncomplicated cases in patients without recent antibiotic exposure, though amoxicillin-clavulanate is increasingly preferred given rising beta-lactamase production 4

Second-Line Treatment Options

If penicillin allergy is documented:

• Cefuroxime axetil: 500 mg twice daily for 10-14 days in adults; this second-generation cephalosporin has significantly enhanced activity against beta-lactamase-producing H. influenzae and M. catarrhalis 1, 3
• Cefpodoxime or cefdinir: Third-generation cephalosporins with appropriate coverage (unlike cefixime and ceftibuten, which have poor S. pneumoniae activity and should be avoided) 1
• Cefalexin is mentioned as an alternative for severe penicillin allergy in regions with high macrolide resistance, but this refers to cephalexin only in the context of pharyngitis, not sinusitis 1

Clinical Evidence Against Cephalexin

While older studies from the 1980s showed some efficacy of cephalexin in sinusitis 5, 6, these findings are superseded by:

• Modern resistance patterns: Current guidelines explicitly state first-generation cephalosporins are inappropriate due to poor H. influenzae coverage 1
• Comparative effectiveness data: Studies demonstrate higher failure rates with cephalosporins lacking beta-lactamase stability compared to amoxicillin-clavulanate 1
• Systematic review findings: Cephalosporins or macrolides show higher risk of clinical failure than amoxicillin-clavulanate (RR 1.37; 95% CI 1.04-1.80) 1

When Antibiotics Are Actually Needed

Most sinusitis cases are viral and do not require antibiotics:

• Symptoms must persist ≥7 days, show severe presentation, or include purulent nasal discharge with maxillary pain/tenderness to warrant antibiotic therapy 7
• Watchful waiting with symptom relief is the recommended first-choice approach for most cases 1
• Approximately 40-60% of cases resolve spontaneously without antibiotics 7

Treatment Duration

• Standard course: 7-10 days for adults and children 3, 4
• Alternative strategy: Continue antibiotics for 7 days after becoming symptom-free (minimum 10 days total) 1
• Shorter courses: Some second- and third-generation cephalosporins (cefuroxime, cefpodoxime) demonstrate efficacy with 5-day courses, though 7-10 days remains standard 3, 8

Critical Pitfalls to Avoid

• Do not prescribe cephalexin for sinusitis: Its poor H. influenzae coverage makes treatment failure likely 1
• Avoid cefixime and ceftibuten: These third-generation agents have inadequate S. pneumoniae coverage, especially against penicillin-resistant strains 1
• Do not use cefaclor: High prevalence of serum sickness-like reactions and inadequate coverage against beta-lactamase-producing organisms make it unattractive 1
• Assess response at 72 hours: If no improvement occurs within 3-5 days on appropriate therapy, switch to high-dose amoxicillin-clavulanate or consider respiratory fluoroquinolones 4, 7