What is the best initial antibiotic for an adult with a peritonsillar abscess who has no penicillin allergy, no severe liver disease, and is not pregnant?

Best Antibiotic for Peritonsillar Abscess

For an adult with peritonsillar abscess without penicillin allergy, amoxicillin-clavulanate is the best initial antibiotic choice, providing coverage for both aerobic streptococci and anaerobic bacteria that commonly cause this infection.

Rationale for Antibiotic Selection

Microbiology of Peritonsillar Abscess

• Peritonsillar abscesses are polymicrobial infections caused by both aerobic and anaerobic bacteria 1, 2
• The predominant organisms are Streptococcus pyogenes (most common aerobic pathogen) and anaerobic bacteria including Bacteroides species 1, 3
• Staphylococcus aureus is isolated in approximately 20-30% of cases, with resistance to penicillin noted 3
• Mixed aerobic-anaerobic flora occurs in approximately 50% of cases 1

First-Line Antibiotic Recommendation

Amoxicillin-clavulanate is the optimal choice because:

• It provides coverage for Streptococcus pyogenes (the most common pathogen) 3
• The clavulanate component covers beta-lactamase producing Staphylococcus aureus, which is penicillin-resistant 3
• It has excellent anaerobic coverage, particularly for Bacteroides species 1
• It is effective as monotherapy without requiring combination regimens 2

Dosing: High-dose amoxicillin-clavulanate (875 mg/125 mg orally twice daily or 2000 mg/125 mg extended-release twice daily) is recommended to ensure adequate coverage 4

Alternative Regimens

If amoxicillin-clavulanate is unavailable or not tolerated:

Penicillin plus metronidazole is an effective combination:

• Penicillin (phenoxymethylpenicillin 4.5 million units per day divided) covers streptococci 1, 5, 6
• Metronidazole (1500 mg per day divided) provides anaerobic coverage 1
• This combination achieved complete recovery in all patients in one study 1

For penicillin-allergic patients:

• Clindamycin 300-450 mg orally every 6-8 hours is the best alternative 2
• Clindamycin provides excellent coverage for both aerobic streptococci and anaerobes as monotherapy 2
• It has good tissue penetration in head and neck infections 4

Critical Management Points

Antibiotics Are Adjunctive to Drainage

• Needle aspiration or incision and drainage is the primary treatment for peritonsillar abscess 2, 5
• Antibiotics alone rarely cure abscesses without source control 7
• Needle aspiration with antibiotics achieved 82% resolution without further intervention 5

When to Avoid Certain Antibiotics

• Penicillin monotherapy should be avoided because Staphylococcus aureus isolates are uniformly resistant 3
• Macrolides (erythromycin, azithromycin) are not recommended due to high resistance rates in streptococci (>40%) 4
• Fluoroquinolones should be reserved for treatment failures, not first-line therapy 4

Duration of Therapy

• 5-7 days of antibiotic therapy is typically sufficient after adequate drainage 2
• Continue until clinical improvement is evident (resolution of fever, trismus, and throat pain) 2

Common Pitfalls to Avoid

• Don't use penicillin alone: While historically recommended, current resistance patterns make monotherapy inadequate 3
• Don't skip drainage: Antibiotics without drainage have high failure rates 7, 2
• Don't delay treatment: Peritonsillar abscess can progress to deep neck space infections if inadequately treated 2
• Don't forget anaerobic coverage: Approximately 75% of cases involve anaerobes, making coverage essential 1