In a healthy 53‑year‑old with acute sinus infection, how many times daily should cephalexin be administered?

Cephalexin Dosing for Acute Sinus Infection in a 53-Year-Old

Cephalexin is not recommended for acute bacterial sinusitis because it provides inadequate coverage against Haemophilus influenzae, a major causative pathogen, with approximately 50% of strains producing β-lactamase that renders cephalexin ineffective. 1

Why Cephalexin Should Not Be Used

• First-generation cephalosporins like cephalexin have poor activity against H. influenzae, which accounts for 30–40% of acute bacterial sinusitis cases alongside Streptococcus pneumoniae and Moraxella catarrhalis. 1

• The American Academy of Allergy, Asthma, and Immunology explicitly contraindicates first-generation cephalosporins for sinusitis based on their inadequate H. influenzae coverage. 1

• Even older studies from the 1980s and 1990s that evaluated cephalexin for sinusitis 2, 3, 4 predate the current understanding of β-lactamase-producing organisms and resistance patterns that now make this agent obsolete for respiratory infections.

Recommended First-Line Treatment Instead

For a healthy 53-year-old with confirmed acute bacterial sinusitis, prescribe amoxicillin-clavulanate 875 mg/125 mg twice daily for 5–10 days (or until symptom-free for 7 consecutive days). 1

Diagnostic Criteria Before Prescribing Antibiotics

• Antibiotics are indicated only when at least one of the following patterns is present:

  • Persistent symptoms ≥10 days without improvement (purulent nasal discharge plus obstruction or facial pain/pressure). 1
  • Severe symptoms ≥3–4 consecutive days with fever ≥39°C, purulent discharge, and facial pain. 1
  • "Double sickening" – initial improvement from a viral URI followed by worsening within 10 days. 1

• Approximately 98–99.5% of acute rhinosinusitis is viral and resolves spontaneously within 7–10 days without antibiotics. 1

Why Amoxicillin-Clavulanate Is Preferred

• Amoxicillin-clavulanate provides 90–92% predicted clinical efficacy against all three major sinusitis pathogens (S. pneumoniae, H. influenzae, M. catarrhalis). 1

• The clavulanate component is essential because 30–40% of H. influenzae and 90–100% of M. catarrhalis produce β-lactamase. 1

Treatment Duration

• Standard course: 5–10 days, or continue until symptom-free for 7 consecutive days (typically 10–14 days total). 1

• Recent evidence supports shorter 5–7 day courses with comparable efficacy and fewer adverse effects. 1, 5

Alternatives for Penicillin Allergy

• Non-severe (non-type I) allergy: Second- or third-generation cephalosporins (cefuroxime-axetil, cefpodoxime-proxetil, cefdinir) for 10 days – cross-reactivity is negligible. 1, 6

• Severe (type I/anaphylactic) allergy: Respiratory fluoroquinolones (levofloxacin 500 mg once daily for 10–14 days or moxifloxacin 400 mg once daily for 10 days) with 90–92% predicted efficacy. 1, 6

• Doxycycline 100 mg once daily for 10 days is an acceptable but suboptimal alternative (77–81% efficacy with 20–25% bacteriologic failure rate). 1, 7

Essential Adjunctive Therapies (Add to All Patients)

• Intranasal corticosteroids (mometasone, fluticasone, or budesonide) twice daily reduce mucosal inflammation and accelerate symptom resolution – supported by strong evidence from multiple randomized controlled trials. 1

• Saline nasal irrigation 2–3 times daily for symptomatic relief and mucus clearance. 1

• Analgesics (acetaminophen or ibuprofen) for pain and fever control. 1

Monitoring and Reassessment

• Reassess at 3–5 days: If no improvement, switch to high-dose amoxicillin-clavulanate (2 g/125 mg twice daily) or a respiratory fluoroquinolone. 1

• Reassess at 7 days: Persistent or worsening symptoms warrant diagnostic reconsideration, exclusion of complications (orbital cellulitis, meningitis), and possible imaging or ENT referral. 1

Critical Pitfalls to Avoid

• Do not prescribe antibiotics for symptoms <10 days unless severe features (fever ≥39°C with purulent discharge for ≥3 consecutive days) are present. 1

• Never use first-generation cephalosporins (cephalexin, cefadroxil) for sinusitis due to inadequate H. influenzae coverage. 1

• Ensure minimum treatment duration of 5 days for adults to prevent relapse. 1