What is the initial antibiotic of choice for peritonsillar abscess?

Initial Antibiotic Therapy for Peritonsillar Abscess

Penicillin plus metronidazole is the recommended initial antibiotic regimen for suspected peritonsillar abscess, as this combination effectively covers both aerobic and anaerobic bacteria commonly found in these infections. 1

Microbiology and Rationale

Peritonsillar abscesses are typically polymicrobial infections involving:

• Aerobic bacteria: Primarily Streptococcus pyogenes (Group A Streptococcus) and Staphylococcus aureus 2
• Anaerobic bacteria: Predominantly Bacteroides species 3

Studies have demonstrated that:

• Mixed aerobic and anaerobic flora are present in approximately 50% of cases 3
• Anaerobes alone are found in about 25% of cases 3
• Aerobic bacteria alone are found in about 25% of cases 3

Recommended Antibiotic Regimen

First-line therapy:

• Penicillin (phenoxymethylpenicillin 4.5 million units daily divided in doses) PLUS
• Metronidazole (1500 mg daily divided in doses) 3, 1

This combination provides:

• Coverage against Streptococcus pyogenes with penicillin
• Coverage against anaerobic bacteria with metronidazole
• Complete recovery has been documented with this regimen 3

Alternative regimens (for penicillin-allergic patients):

• Clindamycin (300-450 mg PO q8h) - effective against both aerobic and anaerobic bacteria 4, 1
• Cephalosporins (if no immediate hypersensitivity to penicillin) plus metronidazole 5

Important Clinical Considerations

1. Drainage is essential: While antibiotics are important, needle aspiration or surgical drainage of the abscess is the primary treatment 5, 6

2. Routine bacterial cultures: Not necessary on initial presentation unless there is treatment failure 3, 1

3. Treatment duration: Typically 7-10 days for uncomplicated cases 4

4. Monitoring response: Clinical improvement should be seen within 48-72 hours of initiating appropriate therapy 4

5. Warning signs requiring immediate attention:

   • Worsening trismus (inability to open mouth)
   • Respiratory distress
   • Extension of infection into deep neck spaces
   • Failure to improve within 48 hours 6

Special Situations

• MRSA concern: If community-acquired MRSA is prevalent in your area or patient has risk factors, consider adding TMP-SMX or switching to clindamycin (after D-test to rule out inducible resistance) 4

• Severe cases: Hospitalization for IV antibiotics may be necessary for patients with systemic symptoms (high fever, tachycardia), extensive infection, or immunocompromise 4

• Recurrent peritonsillar abscess: Consider ENT referral for possible tonsillectomy 4

By targeting both aerobic and anaerobic pathogens with penicillin plus metronidazole, you'll provide optimal coverage for the polymicrobial nature of peritonsillar abscesses while minimizing antibiotic resistance and treatment failure.