Metronidazole for Peritonsillar Abscess
Metronidazole (Flagyl) can be used as part of the antibiotic regimen for peritonsillar abscess, but recent evidence suggests it provides no additional benefit over penicillin alone and may increase side effects. 1
Primary Recommendation
- Penicillin monotherapy is the preferred first-line antibiotic treatment after drainage of peritonsillar abscess. 1
- A systematic review of randomized controlled trials found no evidence supporting additional benefit with metronidazole, while studies demonstrated increased side effects when added to penicillin. 1
When Metronidazole May Be Considered
Despite limited evidence of benefit, metronidazole is still used in certain clinical scenarios:
- Combination therapy with penicillin plus metronidazole (1500 mg per day) has been used successfully in clinical practice, particularly when anaerobic coverage is desired. 2
- One study using phenoxymethylpenicillin (4.5 million units per day) plus metronidazole (1500 mg per day) achieved complete recovery in all patients, though this was not compared to penicillin alone. 2
- Benzylpenicillin plus metronidazole is commonly used for complicated cases, such as parapharyngeal abscess with concomitant peritonsillar abscess. 3
Microbiological Rationale
- Peritonsillar abscesses contain mixed aerobic and anaerobic bacteria, with Streptococcus and Bacteroides being predominant isolates. 2
- Anaerobic bacteria were present in 75% of cases in one series (either alone or mixed with aerobes). 2
- The most commonly isolated bacteria in Denmark are Fusobacterium necrophorum and Streptococcus pyogenes group A. 4
Treatment Algorithm
After surgical drainage (needle aspiration, incision and drainage, or tonsillectomy):
- First-line: Penicillin alone (phenoxymethylpenicillin or benzylpenicillin) 1
- Alternative regimens if penicillin allergy or treatment failure: Clindamycin, cephalosporins, or metronidazole 5
- Duration: Typically 10-14 days of oral therapy 6, 7
Important Clinical Caveats
- Bacteriologic studies are unnecessary on initial presentation in routine management of peritonsillar abscess. 2
- Clinical improvement should be evident within 72 hours; if not, reevaluation is indicated. 6, 7
- Metronidazole causes a disulfiram-like reaction with alcohol, so patients must avoid alcohol during treatment and for 24 hours afterward. 6
- Gastrointestinal side effects are common with metronidazole, potentially affecting compliance. 6, 1
Bottom Line
While metronidazole provides anaerobic coverage and has been used historically for peritonsillar abscess, the best available evidence does not support its routine addition to penicillin therapy. 1 Reserve metronidazole for complicated cases, treatment failures, or when there are specific concerns about inadequate anaerobic coverage in polymicrobial infections. 6