IV Antibiotic Regimen for Cat Bites
For cat bites requiring intravenous antibiotics, use ampicillin-sulbactam (1.5-3.0 g every 6-8 hours) as first-line therapy, with alternative options including piperacillin-tazobactam (3.37 g every 6-8 hours) or carbapenems (ertapenem, imipenem, or meropenem). 1
When IV Antibiotics Are Indicated
IV antibiotics are necessary when cat bites present with:
- Established infection with systemic signs (fever, lymphangitis, significant cellulitis) 1
- Deep tissue involvement including septic arthritis, osteomyelitis, or tenosynovitis 1, 2
- Hand wounds with complications - these carry the highest infection risk and often require admission 2, 3
- Failure of oral antibiotic therapy 1
- Immunocompromised patients with moderate to severe injuries 1
First-Line IV Regimens
The IDSA guidelines provide clear IV options based on coverage of the key pathogens (Pasteurella multocida in 75% of cat bites, anaerobes in 65%, and staphylococci/streptococci in 40%): 1, 2
Beta-lactam/Beta-lactamase Combinations:
- Ampicillin-sulbactam 1.5-3.0 g IV every 6-8 hours 1
- Piperacillin-tazobactam 3.37 g IV every 6-8 hours 1
Second-Generation Cephalosporins:
- Cefoxitin 1 g IV every 6-8 hours 1
Carbapenems (for severe infections):
Critical Pitfalls to Avoid
Never use these agents for cat bites as they have poor activity against P. multocida: 1, 2
- First-generation cephalosporins (cephalexin, cefazolin alone)
- Penicillinase-resistant penicillins (dicloxacillin, nafcillin alone)
- Macrolides (erythromycin, azithromycin)
- Clindamycin monotherapy
Duration of IV Therapy
Treatment duration depends on the complication: 1
- Cellulitis/soft tissue infection: 3-5 days IV, then transition to oral therapy
- Septic arthritis/synovitis: 3-4 weeks total
- Osteomyelitis: 4-6 weeks total
Transition to Oral Therapy
Once clinical improvement occurs (reduced erythema, swelling, pain), transition to amoxicillin-clavulanate 875/125 mg twice daily to complete the treatment course. 1, 2
Special Considerations for Hand Wounds
Cat bites to the hand warrant particular attention: 2, 3
- Pain disproportionate to injury near bone or joint suggests periosteal penetration and requires imaging and possible surgical exploration 1
- Late presentations (>24 hours) with hand bites frequently have tendon involvement or purulent flexor tenosynovitis requiring admission and IV antibiotics 3
- Mean hospital stay for complicated hand infections is 6 days 3
Adjunctive Measures
Beyond antibiotics, essential management includes: 1
- Elevation of the affected extremity to reduce swelling
- Surgical exploration and debridement for deep infections, abscesses, or suspected joint/bone involvement
- Do not primarily close infected wounds - allow healing by secondary intention 1