In an otherwise healthy adult with no drug allergies who develops bacterial sinusitis or bronchitis after a viral upper‑respiratory infection, what oral β‑lactam antibiotic should be prescribed?

Oral β-Lactam Antibiotic for Bacterial Superinfection After Viral URI

For an otherwise healthy adult with bacterial sinusitis or bronchitis following a viral upper respiratory infection, prescribe amoxicillin-clavulanate 875 mg/125 mg twice daily for 5-10 days as the preferred first-line β-lactam antibiotic. 1

Confirming Bacterial Superinfection Before Prescribing

Before initiating antibiotics, verify that the patient meets criteria for acute bacterial rhinosinusitis rather than ongoing viral illness:

• Persistent symptoms ≥10 days without improvement (purulent nasal discharge with nasal obstruction or facial pain/pressure) 1, 2
• Severe symptoms for ≥3-4 consecutive days (fever ≥39°C with purulent nasal discharge and facial pain) 1
• "Double sickening" – worsening after initial improvement from the viral URI 1, 2

Approximately 98-99.5% of acute rhinosinusitis is viral and resolves spontaneously within 7-10 days without antibiotics. 1 Do not prescribe antibiotics for symptoms lasting <10 days unless severe features are present. 1

Why Amoxicillin-Clavulanate Over Plain Amoxicillin

Amoxicillin-clavulanate is preferred over plain amoxicillin due to the increasing prevalence of β-lactamase-producing organisms:

• Approximately 30-40% of Haemophilus influenzae isolates produce β-lactamase 1, 3
• 90-100% of Moraxella catarrhalis produce β-lactamase 1
• The clavulanate component provides coverage against these β-lactamase-producing pathogens while maintaining activity against Streptococcus pneumoniae 3
• Predicted clinical efficacy is 90-92% against the major sinusitis pathogens 1

Plain amoxicillin (500 mg twice daily for mild disease or 875 mg twice daily for moderate disease) remains acceptable for uncomplicated cases without recent antibiotic exposure, but amoxicillin-clavulanate is the more robust first-line choice. 1

Dosing and Duration

• Standard dose: 875 mg/125 mg twice daily 1
• Duration: 5-10 days, or 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

For Acute Bronchitis: A Critical Distinction

For acute bronchitis in healthy adults, antibiotics should NOT be prescribed as a rule. 4

• Bacterial involvement in acute bronchitis in healthy adults is extremely rare (Mycoplasma pneumoniae, Chlamydia pneumoniae, Bordetella pertussis only occasionally) 4
• The clinical course is generally spontaneously favorable after about 10 days 4
• Purulent sputum during acute bronchitis is NOT associated with bacterial superinfection in healthy subjects 4
• Fever persisting more than 7 days would be indicative of bacterial superinfection and warrant antibiotic consideration 4
• The benefit of antibiotic therapy on clinical course or complications has not been confirmed in clinical trials versus placebo 4

If true bacterial bronchitis is confirmed (rare in healthy adults), amoxicillin-clavulanate would be the appropriate β-lactam choice using the same dosing as for sinusitis. 5, 6

Alternatives for Penicillin Allergy

• Non-severe (non-Type I) penicillin allergy: Second- or third-generation cephalosporins are preferred due to negligible cross-reactivity 1
  • Cefuroxime-axetil (second-generation) 1
  • Cefpodoxime-proxetil, cefdinir, or cefprozil (third-generation) 1, 7
• Severe (Type I/anaphylactic) penicillin allergy: Respiratory fluoroquinolones 1
  • Levofloxacin 500 mg once daily for 10-14 days 1
  • Moxifloxacin 400 mg once daily for 10 days 1

Essential Adjunctive Therapies

Add these to antibiotic therapy to improve outcomes:

• Intranasal corticosteroids (mometasone, fluticasone, or budesonide) twice daily – reduce mucosal inflammation and accelerate symptom resolution (strong evidence from multiple RCTs) 1
• Saline nasal irrigation 2-3 times daily – provides symptomatic relief and clears mucus 1
• Analgesics (acetaminophen or ibuprofen) – for pain and fever control 1

Monitoring and Treatment Failure Protocol

• 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: If symptoms persist or worsen, reconfirm diagnosis, exclude complications (orbital cellulitis, meningitis), and consider imaging or ENT referral 1

Critical Pitfalls to Avoid

• Do not use azithromycin or other macrolides – resistance rates exceed 20-25% for both S. pneumoniae and H. influenzae 1
• Do not use trimethoprim-sulfamethoxazole – 50% resistance in S. pneumoniae and 27% in H. influenzae 1
• Do not use first-generation cephalosporins (cephalexin) – inadequate coverage against H. influenzae due to β-lactamase production 1
• Reserve fluoroquinolones for treatment failures or documented severe β-lactam allergies to prevent resistance development 1
• Gastrointestinal adverse effects are more common with amoxicillin-clavulanate (diarrhea in 40-43% of patients); counsel patients accordingly 1