What is the recommended dose of cefalexin (cephalexin) for upper respiratory tract infections?

Cefalexin Dosing for Upper Respiratory Tract Infections

Cefalexin is NOT recommended as first-line therapy for upper respiratory tract infections due to inadequate coverage of common respiratory pathogens, particularly Haemophilus influenzae and penicillin-resistant Streptococcus pneumoniae. 1, 2

Why Cefalexin Should Be Avoided

• First-generation cephalosporins like cefalexin have poor coverage for H. influenzae, which is a major pathogen in sinusitis and other URTIs, with failure rates approaching 50% in H. influenzae infections 1, 3
• Cefalexin lacks adequate activity against beta-lactamase-producing organisms, which now represent nearly 50% of H. influenzae and 90-100% of M. catarrhalis strains 1
• Current guidelines explicitly state that first-generation cephalosporins should not be used for respiratory infections due to inadequate pathogen coverage 2

Appropriate First-Line Alternatives

For Adults with Bacterial Sinusitis or URTI:

• Amoxicillin-clavulanate 875/125 mg twice daily for 7-10 days is the preferred first-line agent 1, 2
• Second-generation cephalosporins (cefuroxime-axetil 250-500 mg twice daily) provide better coverage than cefalexin 1
• Third-generation cephalosporins like cefpodoxime-proxetil or cefdinir are suitable alternatives 1

For Pediatric Patients:

• Amoxicillin-clavulanate 80 mg/kg/day (based on amoxicillin component) in three divided doses, not exceeding 3 g/day 1, 2
• Cefpodoxime-proxetil 8 mg/kg/day in two doses for 7-10 days 1

If Cefalexin Must Be Used (Not Recommended)

The FDA-approved dosing for cefalexin is 250 mg every 6 hours for adults, or 500 mg every 12 hours for streptococcal pharyngitis specifically 4. However, this should only be considered for:

• Confirmed Group A streptococcal pharyngitis where penicillin allergy exists and other options are unavailable 4, 3
• Pediatric dosing: 25-50 mg/kg/day in divided doses, with streptococcal pharyngitis requiring at least 10 days of therapy 4

Critical Clinical Pitfalls

• Do not prescribe antibiotics for viral URIs, as they cause more harm than benefit and most URTIs are viral 2
• Antibiotics are only indicated when symptoms persist beyond 10 days without improvement, or with severe symptoms (fever >39°C with purulent discharge for ≥3 consecutive days) 2
• The "double sickening" pattern (worsening after initial improvement) is another key indicator for bacterial infection requiring antibiotics 2

Treatment Duration and Monitoring

• Standard treatment duration is 7-10 days for most bacterial URTIs 1
• Assess therapeutic efficacy after 2-3 days of treatment 2
• Fever should resolve within 24 hours for pneumococcal infections and 2-4 days for other bacterial etiologies 2