## First-Line Antibiotic for Acute Bacterial Tonsillitis **Key Point:** Amoxicillin-clavulanic acid is the gold standard first-line agent for acute bacterial tonsillitis in both children and adults. ### Rationale for Amoxicillin-Clavulanic Acid **High-Yield:** The combination covers the three most common causative organisms: - *Streptococcus pyogenes* (Group A Streptococcus) — ~30% of cases - *Staphylococcus aureus* — ~20% of cases - *Haemophilus influenzae* — ~10% of cases The clavulanic acid component inhibits β-lactamase produced by *S. aureus* and *H. influenzae*, preventing resistance. ### Dosing in Adults - Amoxicillin-clavulanic acid: 500/125 mg three times daily for 7–10 days (oral) - Or 875/125 mg twice daily (extended-release formulation) **Clinical Pearl:** In penicillin-allergic patients, second-generation cephalosporins (cephalexin) or macrolides (azithromycin) are acceptable alternatives, though cross-reactivity with cephalosporins is <2% in non-anaphylactic penicillin allergy. ### Why This Agent? | Feature | Amoxicillin-Clavulanic Acid | Cephalexin | Erythromycin | Ciprofloxacin | |---------|------------------------------|-----------|--------------|---------------| | Coverage of *S. pyogenes* | Excellent | Good | Moderate | Poor | | Coverage of *S. aureus* (β-lactamase+) | Excellent | Good | Moderate | Good | | Coverage of *H. influenzae* | Excellent | Good | Moderate | Good | | First-line status | Yes | Alternative | Alternative | No | | Oral bioavailability | Excellent | Good | Good | Excellent | **Warning:** Fluoroquinolones (ciprofloxacin) are NOT first-line for tonsillitis; they are reserved for resistant gram-negative infections and should be avoided in uncomplicated acute tonsillitis due to concerns about resistance development. [cite:Harrison 21e Ch 139]
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