What is the best oral (PO) antibiotic for a 60-year-old male with a sacral wound infected with Rusobacterium nucleatum and Prevotella spp.?

Oral Antibiotic for Sacral Wound with Fusobacterium nucleatum and Prevotella spp.

Amoxicillin-clavulanate 875/125 mg twice daily is the best oral antibiotic for this polymicrobial sacral wound infection with anaerobes (Fusobacterium nucleatum and Prevotella spp.).

Rationale for Antibiotic Selection

Coverage Requirements for This Infection

This sacral wound infection requires coverage of both anaerobic organisms identified:

• Fusobacterium nucleatum is a gram-negative anaerobe commonly found in oral flora but can cause invasive infections including abscesses and osteomyelitis 1, 2
• Prevotella spp. are anaerobic gram-negative bacilli frequently isolated from polymicrobial wound infections, particularly in sacral pressure injuries 3
• Polymicrobial infections involving these organisms are expected in sacral wounds due to fecal contamination and biofilm formation 3

First-Line Oral Agent

Amoxicillin-clavulanate is the preferred oral agent because:

• It provides excellent coverage against both Fusobacterium nucleatum and Prevotella spp. 3
• All Fusobacterium isolates in clinical studies were susceptible to penicillin-based antibiotics 1
• The beta-lactamase inhibitor (clavulanate) is essential because many anaerobes including Prevotella spp. produce beta-lactamases, making them resistant to penicillin alone 3
• It is specifically recommended for human bite wounds (which have similar polymicrobial anaerobic flora including Fusobacterium and Prevotella) 3

Alternative Oral Regimens

If the patient has a penicillin allergy or amoxicillin-clavulanate is not tolerated:

• Moxifloxacin 400 mg once daily as monotherapy provides broad anaerobic coverage 3, 4

  • Successfully used to treat Fusobacterium nucleatum infections in combination with metronidazole 5
  • Has excellent activity against anaerobes including Prevotella spp. 3

• Combination therapy with a fluoroquinolone plus metronidazole (e.g., ciprofloxacin 500-750 mg twice daily or levofloxacin 750 mg daily PLUS metronidazole 500 mg three times daily) 3

  • Provides comprehensive aerobic and anaerobic coverage
  • Metronidazole has the greatest spectrum against gram-negative anaerobes 3

• Clindamycin 300 mg three times daily 3

  • Good activity against anaerobes including Fusobacterium and Prevotella 3
  • However, misses some gram-negative organisms that may be present 3

Treatment Duration and Clinical Context

Determining Need for Systemic Antibiotics

The decision to treat depends on clinical presentation 3:

• Systemic signs of infection present (fever >38.5°C, tachycardia >100 bpm, elevated WBC): Initiate oral antibiotics 3
• Local signs only (erythema <5 cm, no systemic symptoms): May not require antibiotics if wound can be adequately debrided 3
• Stage IV pressure injury without soft tissue infection: No systemic antibiotics recommended 3

Duration of Therapy

Based on clinical syndrome 3:

• Skin and soft tissue infection without abscess: 5 days, can extend if slow improvement 3
• Cutaneous abscess: 5-10 days following drainage 3
• Deeper infection (pyomyositis): 14-21 days with drainage 3
• If osteomyelitis suspected and surgery planned: 6 weeks post-operatively 3

Successful Treatment Case Example

A documented case of Fusobacterium nucleatum infection was successfully treated with moxifloxacin and metronidazole following abscess drainage 5, and another case achieved cure with ampicillin-sulbactam IV followed by oral amoxicillin-clavulanate for 8 weeks for osteomyelitis 6.

Important Clinical Considerations

Surgical Management

• Debridement is critical if necrotic tissue is present 3
• Antibiotics alone are insufficient without source control 3
• Deep tissue cultures (not swabs) provide the most accurate microbiology 3

Polymicrobial Nature

• Expect co-infection with other organisms including Staphylococcus aureus, Streptococcus spp., and other anaerobes 3, 1
• Consider MRSA coverage if local epidemiology suggests high prevalence 3
• The chosen regimen (amoxicillin-clavulanate) covers the identified organisms but may need broadening if clinical response is inadequate 3

Monitoring Response

• Clinical improvement should be evident within 48-72 hours 3
• Lack of response warrants imaging to evaluate for deeper infection (osteomyelitis) or abscess requiring drainage 3
• Consider hospitalization for IV antibiotics if oral therapy fails or patient has severe systemic toxicity 3