Second-Line Treatment for Cat Bite After Augmentin Failure
For cat bite infections that have failed amoxicillin-clavulanate (Augmentin), switch to either moxifloxacin 400 mg daily as monotherapy OR doxycycline 100 mg twice daily, both given orally. These are the most appropriate second-line options based on IDSA guidelines for animal bite infections 1.
Rationale for Second-Line Selection
The 2014 IDSA guidelines for skin and soft tissue infections provide a comprehensive table of antibiotic options for animal bites 1. When Augmentin fails, you need to consider:
Why These Options Work:
Moxifloxacin is specifically highlighted in the guidelines as monotherapy with good anaerobic coverage—a critical advantage since cat bites involve both aerobic (Pasteurella multocida) and anaerobic organisms 1. The 400 mg daily dosing provides:
- Excellent activity against P. multocida (the primary pathogen in cat bites)
- Comprehensive anaerobic coverage without needing combination therapy
- Once-daily dosing that improves compliance
Doxycycline offers excellent activity against Pasteurella multocida specifically 1. The guidelines note it has "excellent activity against Pasteurella multocida" though some streptococci may be resistant 1. The 100 mg twice daily dosing is standard.
Alternative Second-Line Options
If fluoroquinolones or tetracyclines are contraindicated, consider these combinations from the IDSA guidelines 1:
- Ceftriaxone 1 g every 12 hours IV (third-generation cephalosporin with good P. multocida activity)
- Levofloxacin 750 mg daily (alternative fluoroquinolone)
- Combination therapy: SMX-TMP 160-800 mg twice daily PLUS metronidazole 250-500 mg three times daily (covers aerobes and anaerobes respectively) 1
Critical Pitfalls to Avoid
Do NOT use clindamycin alone—while it has good activity against staphylococci, streptococci, and anaerobes, the guidelines explicitly state it "misses P. multocida" 1. This is the most common pathogen in cat bites with approximately 90% carriage rate in feline oral cavities 2.
Avoid second-generation cephalosporins as monotherapy (like cefuroxime)—they have good P. multocida activity but miss anaerobes 1.
When to Escalate to IV Therapy
If the patient has systemic signs of infection, severe local infection, or cannot tolerate oral medications, switch to IV options 1:
- Ampicillin-sulbactam 1.5-3.0 g every 6-8 hours IV
- Piperacillin-tazobactam 3.37 g every 6-8 hours IV
- Carbapenems (see individual dosing)
Note: All beta-lactam/beta-lactamase inhibitor combinations and carbapenems miss MRSA 1, so if MRSA is suspected or confirmed, add vancomycin.
Additional Management Considerations
Beyond antibiotic selection, ensure:
- Wound reassessment: Failure may indicate inadequate surgical debridement, abscess formation, or retained foreign body requiring imaging
- Culture and susceptibility testing: Should be obtained before switching antibiotics when possible to guide definitive therapy
- Duration: Typically 7-10 days for uncomplicated infections, longer for deeper infections or osteomyelitis
The high susceptibility of P. multocida to penicillins (100% to amoxicillin-clavulanate in one study) 2 suggests true Augmentin failure may indicate either resistant organisms, inadequate source control, or non-Pasteurella pathogens requiring broader coverage.