Cefalexin Should NOT Be Used for Rat Bite Wounds
Do not give cefalexin (cephalexin) for rat bite wounds—first-generation cephalosporins have poor activity against Pasteurella multocida and should be avoided. 1
Recommended Antibiotic Choice
Amoxicillin-clavulanate is the first-line antibiotic for animal bite wounds, including rat bites. 1
- Oral dosing: Amoxicillin-clavulanate 500 mg every 8 hours 1
- This provides coverage against the polymicrobial flora typical of animal bites, including Pasteurella species, staphylococci, streptococci, and anaerobes 1
Why Cefalexin Fails
The Infectious Diseases Society of America explicitly states that first-generation cephalosporins like cephalexin should be avoided (D-III recommendation) because they have poor in vitro activity against Pasteurella multocida, which is isolated from 50% of dog bites and 75% of cat bites. 1
Critical pitfall: While cefalexin covers staphylococci and streptococci adequately, it completely misses P. multocida and anaerobes—both common pathogens in rodent bites. 1
Alternative Regimens (If Penicillin Allergy)
If the patient cannot take amoxicillin-clavulanate:
- Doxycycline 100 mg twice daily has excellent activity against Pasteurella multocida 1
- Combination therapy: Penicillin VK 500 mg four times daily PLUS dicloxacillin 500 mg four times daily 1
- Fluoroquinolones (ciprofloxacin 500-750 mg twice daily, levofloxacin, or moxifloxacin) PLUS metronidazole for anaerobic coverage 1
Note: Fluoroquinolones have good activity against P. multocida but miss some anaerobes, requiring the addition of metronidazole or clindamycin. 1
Intravenous Options (For Severe Infections)
If hospitalization is required:
- Ampicillin-sulbactam 1.5-3.0 g every 6 hours 1
- Piperacillin-tazobactam 1
- Second-generation cephalosporins (cefoxitin, cefuroxime) have better P. multocida coverage than first-generation agents 1
- Carbapenems (ertapenem, imipenem, meropenem) 1
Essential Adjunctive Measures
Beyond antibiotics, proper wound management is critical:
- Cleanse with sterile normal saline (no iodine or antibiotic solutions needed) 1
- Do not close infected wounds 1
- Elevate the injured body part if swollen 1
- Update tetanus prophylaxis if not current within 10 years 1, 2
- Consider rabies prophylaxis for wild or feral animal bites after consulting local health department 1
Treatment Duration
- Standard prophylaxis or treatment: 3-5 days 1, 2
- Complicated infections (osteomyelitis): 4-6 weeks 1
- Septic arthritis: 3-4 weeks 1
High-Risk Situations Requiring Antibiotics
The Infectious Diseases Society of America recommends preemptive antibiotic therapy for patients with: 2
- Immunocompromised status
- Asplenia (risk of Capnocytophaga canimorsus sepsis) 1
- Advanced liver disease
- Moderate to severe injuries, especially to hand or foot
- Injuries penetrating periosteum or joint capsule
Hand wounds are particularly serious and warrant aggressive treatment due to higher risk of complications including septic arthritis and osteomyelitis. 1