What antibiotic should be given for a rat bite?

Antibiotic Therapy for Rat Bites

For rat bites, amoxicillin-clavulanate 875/125 mg twice daily is the first-line antibiotic when treatment is indicated, providing coverage against the polymicrobial aerobic and anaerobic bacteria commonly found in these wounds. 1

When to Treat with Antibiotics

The decision to use antibiotics for rat bites should be risk-stratified rather than routine:

• High-risk wounds requiring antibiotics include: 1

  • Puncture wounds (which are common with rat bites) 2
  • Wounds involving the hand, face, or areas near joints 1
  • Wounds with signs of infection 1
  • Immunocompromised patients 1
  • Wounds presenting >8-12 hours after injury 1

• Low-risk wounds may not require antibiotics: 3

  • Superficial scratches (Type I wounds) have a very low infection rate (2% in one study) 3
  • These can be managed with wound care alone 4, 3

Important caveat: While older data suggested rat bites have low infection rates, more recent microbiological studies show these wounds are often polymicrobial with both aerobic and anaerobic bacteria, making the deep puncturing nature of rat bites inherently high-risk. 2

First-Line Antibiotic Regimens

Oral Therapy (for outpatient management):

• Amoxicillin-clavulanate 875/125 mg twice daily 1, 5
  • Provides broad coverage against Staphylococcus, Streptococcus, anaerobes, and gram-negative organisms 1
  • Note: May miss MRSA 1

Alternative for Penicillin Allergy:

• Doxycycline 100 mg twice daily 1, 5
  • Good activity against many rat bite pathogens 1
  • Some streptococci may be resistant 1

Intravenous Therapy (for severe infections):

• Ampicillin-sulbactam 1.5-3.0 g every 6-8 hours 1, 5
  • Used successfully in documented rat bite fever cases 6

Duration of Treatment

• Prophylaxis for high-risk wounds: 3-5 days 5
• Established infections: 7-10 days 5
• Complicated infections (septic arthritis): 3-4 weeks 1
• Osteomyelitis: 4-6 weeks 1

Microbiology Considerations

Rat bite wounds contain diverse bacterial flora:

• Most common isolates: Staphylococcus aureus (most frequent), Staphylococcus epidermidis 3, 2
• Polymicrobial infections occur in 72.5% of cases 2
• Other organisms include: Streptobacillus moniliformis (rat bite fever), Streptococcus species, anaerobes, and various gram-negative bacteria 6, 2
• Approximately 22 different bacterial species from 18 genera have been identified 2

Essential Wound Management

Beyond antibiotics, proper wound care is critical:

• Copious irrigation with sterile normal saline using a 20-mL or larger syringe 1, 7
• Wound exploration for foreign bodies, tendon, or bone involvement 7
• Debridement only if infected (Type II wounds) or tissue loss (Type III wounds) 4
• Avoid primary closure of infected wounds 1
• Elevation of injured extremity to reduce swelling 1

Additional Prophylaxis Requirements

• Tetanus prophylaxis: 0.5 mL intramuscularly if status outdated or unknown 1, 3
• Rabies prophylaxis: Generally not required for domestic rat bites, but consult local health officials 1

Common Pitfalls to Avoid

• Delaying antibiotic therapy in high-risk wounds (puncture wounds, hand/face involvement, immunocompromised patients) can lead to serious complications including septic arthritis and osteomyelitis 1, 5
• Using antibiotics without anaerobic coverage (such as first-generation cephalosporins alone or clindamycin monotherapy) will miss important pathogens 1
• Inadequate wound irrigation is a critical error—thorough cleansing is as important as antibiotic selection 1, 5, 7
• Routine antibiotic use for all rat bites is unnecessary; superficial scratches without high-risk features can be managed conservatively 4, 3
• Missing MRSA coverage in severe infections or immunocompromised patients—consider adding vancomycin if MRSA is suspected 1, 5