What is the recommended antibiotic regimen and duration for a peritonsillar abscess, including options for patients with penicillin allergy or high MRSA risk, and the need for drainage?

Antibiotic Treatment for Peritonsillar Abscess

Drainage plus penicillin-based antibiotics remain the cornerstone of peritonsillar abscess treatment, with penicillin alone showing equivalent efficacy to broad-spectrum regimens in most cases.

Primary Treatment Approach

Drainage is essential and must be performed before or concurrent with antibiotic therapy. 1 Antibiotics alone without drainage frequently fail regardless of the agent chosen. 2 The infection is polymicrobial, typically involving Group A Streptococcus and oral anaerobes. 1

First-Line Antibiotic Regimens

Standard Therapy (No Penicillin Allergy)

Penicillin plus metronidazole is the recommended first-line regimen:

• Phenoxymethylpenicillin 4.5 million units per day (or 500 mg QID) PLUS metronidazole 500 mg TID 3, 4
• This combination provides coverage against both aerobic streptococci and anaerobic bacteria, which are present in mixed infections in approximately 50% of cases 3

Alternative monotherapy option:

• Amoxicillin-clavulanate 875/125 mg BID provides broader coverage including anaerobes in a single agent 2

Parenteral Therapy (If Required)

For patients requiring IV antibiotics after drainage:

• Intravenous penicillin alone (penicillin G 2-4 million units IV every 4-6 hours) is as effective as broad-spectrum regimens 5
• A retrospective study of 103 patients showed no statistical difference in hours hospitalized (44.3 vs 38.3 hours, p=0.222) or hours febrile (16.9 vs 13.3 hours, p=0.269) between broad-spectrum antibiotics and penicillin alone 5

Penicillin Allergy Options

For patients with documented penicillin allergy:

• Clindamycin 300-450 mg PO TID or 600 mg IV every 8 hours provides excellent coverage against both Streptococcus (including Group A) and anaerobes 2, 4
• Clindamycin is particularly valuable as it covers both aerobic and anaerobic organisms in a single agent 4

Alternative for severe allergy:

• Linezolid 600 mg PO/IV BID is effective against streptococci, though more expensive 2

MRSA Considerations

MRSA is NOT a typical pathogen in peritonsillar abscess. 6 The predominant organisms are Streptococcus pyogenes and oral anaerobes. 3, 6 However, if Staphylococcus aureus is cultured and shows resistance:

• Clindamycin 300-450 mg PO TID (if susceptible) 2
• TMP-SMX 1-2 double-strength tablets BID (note: limited activity against β-hemolytic streptococci, so should be combined with coverage for streptococci) 2

Treatment Duration

5-10 days of antibiotic therapy is recommended after adequate drainage. 2 Treatment should be extended only if signs of infection persist beyond this period. 2

Critical Management Points

Drainage is Non-Negotiable

• Needle aspiration or incision and drainage must be performed 1
• Delaying drainage results in treatment failure regardless of antibiotic choice 2

Microbiologic Testing

• Routine cultures are unnecessary on initial presentation 3, 4
• Culture should be obtained only if initial therapy fails or in immunocompromised patients

Common Pitfall to Avoid

Do not use penicillin monotherapy if Staphylococcus aureus is suspected or confirmed, as all S. aureus isolates in one study showed penicillin resistance. 6 However, S. aureus is less common than Streptococcus pyogenes in peritonsillar abscess. 6

Clinical Algorithm

1. Perform drainage immediately (aspiration or incision) 1
2. Start penicillin + metronidazole OR amoxicillin-clavulanate 3, 4, 2
3. If penicillin allergic: use clindamycin 2, 4
4. If no improvement in 48-72 hours: consider culture and switch to clindamycin if not already prescribed 4
5. Continue antibiotics for 5-10 days total 2