Antibiotic Management for Rat Bites
Primary Recommendation
For rat bites, prophylactic antibiotics are generally NOT recommended for clean, uninfected wounds presenting within 24 hours, as the infection rate is only 2%; however, if infection develops or high-risk features are present, treat with amoxicillin-clavulanate 875/125 mg twice daily orally for 7-10 days. 1, 2
Risk Stratification and Initial Assessment
Low-Risk Wounds (No Antibiotics Needed)
- Clean, superficial scratches or bites without signs of infection have only a 2% infection rate and do not require prophylactic antibiotics 2
- Most rat bites (72%) occur during sleep and involve exposed areas of upper extremities and face 2
- Treatment should focus on thorough wound cleansing with sterile saline and local wound care 3
High-Risk Features Requiring Antibiotics
- Immunocompromised status, advanced liver disease, or asplenia 4
- Deep puncture wounds or wounds with tissue damage 4, 3
- Wounds involving hands, feet, face, genitals, or near joints 4
- Wounds that may have penetrated periosteum or joint capsule 4
- Pre-existing or resultant edema of the affected area 4
- Clinical signs of infection: erythema, warmth, purulent drainage, or systemic symptoms 1, 3
Antibiotic Selection Algorithm
For Oral Therapy (Outpatient Management)
First-line: Amoxicillin-clavulanate 875/125 mg twice daily 1, 4
- Provides coverage for Staphylococcus, Streptococcus, and anaerobes
- Note: Some gram-negative rods may be resistant; misses MRSA 1
Alternative options if penicillin-allergic:
- Doxycycline 100 mg twice daily (excellent activity against Pasteurella multocida, though some streptococci resistant) 1
- Moxifloxacin 400 mg daily as monotherapy (good anaerobic coverage) 1, 4
- Clindamycin 300 mg three times daily PLUS a fluoroquinolone (covers staphylococci, streptococci, and anaerobes but misses Pasteurella) 1, 4
For Intravenous Therapy (Severe Infections)
Indications for IV therapy: Systemic symptoms, moderate to severe infections, or high-risk wounds 4
First-line IV options:
- Ampicillin-sulbactam 1.5-3.0 g every 6-8 hours 1
- Piperacillin-tazobactam 3.37 g every 6-8 hours 1, 4
- Carbapenems (ertapenem 1 g daily, imipenem 1 g every 6-8 hours, or meropenem 1 g every 8 hours) 1, 4
Alternative IV options:
- Ceftriaxone 1 g every 12 hours PLUS metronidazole 500 mg every 8 hours 1, 4
- Cefoxitin 1 g every 6-8 hours 1, 4
Treatment Duration
- Uncomplicated infections: 7-10 days total 4
- Initial IV therapy: 3-5 days, then transition to oral when afebrile with clinical improvement 4
- Septic arthritis: 3-4 weeks 4
- Osteomyelitis: 4-6 weeks 4
- Hand wounds often require longer treatment due to serious nature 4
Critical Pitfalls to Avoid
- Never use first-generation cephalosporins, macrolides, or penicillinase-resistant penicillins alone - these have poor activity against Pasteurella multocida (present in 50% of animal bites) 4
- Do not prescribe prophylactic antibiotics for wounds presenting >24 hours after bite without signs of infection - this violates guidelines and promotes resistance 4
- Avoid primary wound closure when possible - suturing should be avoided to reduce infection risk 1
- Do not overlook tetanus prophylaxis - most rat bite patients are deficient in tetanus immunization 2
Special Considerations
Rat Bite Fever (Streptobacillus moniliformis)
- If systemic illness develops with fever, rash, and migratory polyarthritis, suspect rat bite fever 5, 6
- Treatment requires penicillin G 12-20 million units/day IV in divided doses every 4 hours for 3-4 weeks 7, 8
- Penicillin is highly effective as first-line therapy for this specific complication 8, 6
Wound Management Essentials
- Thorough wound cleansing with water or dilute povidone-iodine solution markedly decreases bacterial infection risk 1
- Surgical intervention only indicated for drainage of pus, debridement, or skin grafting in full-thickness injuries 3
- Tetanus prophylaxis is mandatory if vaccination not up to date 1, 2
- Rabies prophylaxis usually not required for rat bites, but consult local health officials 1, 4