Keflex (Cephalexin) is NOT Appropriate for Cat Bite Prophylaxis
Cephalexin should be avoided for cat bite wounds because it has poor in vitro activity against Pasteurella multocida, the pathogen isolated from 75% of cat bite wounds, and lacks adequate anaerobic coverage for the polymicrobial flora typically present. 1
Why Cephalexin Fails for Cat Bites
Critical Coverage Gaps
First-generation cephalosporins like cephalexin (Keflex) have poor activity against P. multocida, which is the most common pathogen in cat bite wounds and causes serious infections with severe complications. 1
Cat bite wounds contain an average of 5 different aerobic and anaerobic bacteria, including P. multocida (75% of cases), staphylococci, streptococci, Bacteroides species, fusobacteria, Porphyromonas species, and peptostreptococci—cephalexin does not provide adequate coverage for this polymicrobial mix. 1
The Infectious Diseases Society of America explicitly states that first-generation cephalosporins should be avoided (D-III recommendation) for animal bite wounds due to inadequate P. multocida coverage. 1
Recommended First-Line Therapy Instead
Amoxicillin-Clavulanate is the Gold Standard
Amoxicillin-clavulanate 875/125 mg twice daily for 3-5 days is the recommended first-line prophylaxis for cat bite wounds, providing comprehensive coverage against P. multocida, staphylococci, streptococci, and anaerobes. 1, 2
This regimen has been studied in clinical trials and demonstrates significant reduction in infection rates compared to placebo or inadequate antibiotics. 1, 2
Research confirms that approximately 90% of domestic cats carry P. multocida in their oral cavity, and these isolates show 100% susceptibility to amoxicillin-clavulanate. 3
Alternative Regimens (When Amoxicillin-Clavulanate Cannot Be Used)
For Penicillin Allergy
Doxycycline 100 mg twice daily has excellent activity against P. multocida and provides reliable coverage of staphylococci and anaerobes, though some streptococci may be resistant. 1, 2
For severe penicillin allergies, use fluoroquinolone (ciprofloxacin 500-750 mg twice daily or levofloxacin 750 mg daily) PLUS metronidazole or clindamycin to ensure both aerobic and anaerobic coverage. 1, 2
Other Agents to Avoid
Penicillinase-resistant penicillins (dicloxacillin), macrolides (erythromycin), and clindamycin monotherapy all have poor P. multocida activity and should not be used as single agents. 1, 2
Trimethoprim-sulfamethoxazole has good aerobic activity but poor anaerobic coverage and requires combination with metronidazole if used. 1
Clinical Context: When Prophylaxis is Indicated
High-Risk Features Requiring Antibiotics
Prophylactic antibiotics are indicated for deep puncture wounds, wounds on hands/feet/face/near joints, immunocompromised patients, and wounds presenting >8-12 hours after injury. 1, 2
Cat bites have higher infection rates (20-80%) compared to dog bites (3-18%), with greater prevalence of anaerobes (65% vs 50%) and P. multocida (75% vs 50%). 1, 3
Hand wounds from cat bites have the highest risk of infection and complications, including osteomyelitis and septic arthritis, making prophylactic antibiotics particularly important. 2, 4
Common Pitfall to Avoid
The most common error is prescribing cephalexin because it "covers skin flora"—this approach misses the unique polymicrobial nature of cat bite wounds and the critical role of P. multocida. Unlike typical skin and soft tissue infections where cephalexin is appropriate, cat bites require specific coverage for oral flora from the biting animal. 1