What antibiotics are recommended for a cat bite?

Antibiotic Treatment for Cat Bites

Amoxicillin-clavulanate (875/125 mg twice daily) is the first-line antibiotic for cat bite wounds, whether for prophylaxis of fresh wounds or treatment of established infection. 1, 2

Why Amoxicillin-Clavulanate is First-Line

• Pasteurella multocida is isolated in 70-75% of infected cat bite wounds and requires specific coverage 3, 4, 5
• Amoxicillin-clavulanate provides excellent activity against P. multocida (100% susceptibility), staphylococci, streptococci, and anaerobic organisms that comprise the polymicrobial flora of cat bites 1, 4
• The average cat bite wound yields 5 different bacterial isolates, with approximately 60% having mixed aerobic and anaerobic bacteria 2
• Anaerobic bacteria (including Bacteroides species) are present in 65% of cat bites and require beta-lactamase inhibitor coverage 2, 3

Alternative Oral Regimens for Penicillin Allergy

• Doxycycline 100 mg twice daily has excellent activity against P. multocida, though some streptococci may be resistant 1, 2
• Fluoroquinolones (ciprofloxacin 500-750 mg twice daily, moxifloxacin 400 mg daily, or levofloxacin) provide good P. multocida coverage but miss MRSA and some anaerobes 1, 2
• For severe penicillin allergies, consider combining doxycycline or a fluoroquinolone with metronidazole (250-500 mg four times daily) to ensure anaerobic coverage 1

Antibiotics to AVOID

• First-generation cephalosporins (cephalexin, cefazolin) miss P. multocida and anaerobes 1, 2
• Penicillinase-resistant penicillins (dicloxacillin, nafcillin) have poor P. multocida activity 2
• Macrolides (azithromycin, erythromycin) have insufficient anaerobic coverage and documented clinical failures against P. multocida 2
• Clindamycin monotherapy misses P. multocida entirely 1, 2
• TMP-SMZ has poor anaerobic activity 1

Intravenous Therapy for Severe Infections

• Ampicillin-sulbactam (1.5-3.0 g every 6-8 hours IV) is first-line for hospitalized patients with systemic signs (fever, lymphangitis, significant cellulitis) 1, 2
• Piperacillin-tazobactam (3.37 g every 6-8 hours IV) is an alternative for severe infections 1, 2
• Carbapenems (ertapenem 1 g daily, imipenem 1 g every 6-8 hours, or meropenem 1 g every 8 hours) are reserved for the most severe infections, though they miss MRSA 1, 2

Treatment Duration

• Uncomplicated cellulitis or soft tissue infection: 7-10 days total 1, 6, 7
• Deep tissue involvement with IV therapy: 3-5 days IV, then transition to oral amoxicillin-clavulanate to complete course 2
• Septic arthritis or synovitis: 3-4 weeks total 2
• Osteomyelitis: 4-6 weeks total 2

High-Risk Wounds Requiring Special Attention

• Hand bites have the highest infection risk and complication rate, including tendosynovitis, septic arthritis, and osteomyelitis 2, 7, 5
• Complications occur in approximately 18% of infected cat bite patients, including abscess formation, tendonitis, bacteremia, and meningitis 2, 5
• Symptoms of infection can emerge as early as 3 hours after the bite, with erythema, pain, and edema being the dominant early signs 5

Critical Pitfalls to Avoid

• Never use monotherapy with agents that lack P. multocida coverage - this is the most common pathogen and requires specific targeting 2, 4, 5
• Always order both aerobic AND anaerobic cultures for infected wounds, as anaerobes are present in the majority of cases 3
• Do not primarily close infected wounds - these should heal by secondary intention with elevation of the affected extremity 2
• Approximately 90% of cats carry P. multocida in their oral cavity, making prophylactic antibiotics appropriate for all fresh cat bite wounds considered at risk 4