Best Antibiotic for Animal Bite-Associated Cellulitis
Amoxicillin-clavulanate 875/125 mg twice daily is the best initial antibiotic for cellulitis secondary to an animal bite, providing single-agent coverage against the polymicrobial oral flora including Pasteurella multocida, streptococci, staphylococci, and anaerobes. 1
First-Line Treatment
Oral amoxicillin-clavulanate 875/125 mg twice daily for 5 days is the recommended first-line therapy for animal bite-associated cellulitis. 1 This combination provides comprehensive coverage without requiring multiple antibiotics, as it targets:
- Pasteurella multocida (the predominant pathogen in cat bites, present in 72% of cases) 2
- Beta-hemolytic streptococci 1
- Methicillin-sensitive Staphylococcus aureus 1
- Anaerobic bacteria from oral flora 1
The clavulanate component protects amoxicillin from beta-lactamase degradation, though beta-lactamase-producing P. multocida isolates remain rare. 3
Treatment Duration
Treat for 5 days if clinical improvement occurs; extend only if symptoms have not improved within this timeframe. 1, 4 Traditional 7-14 day courses are no longer necessary for uncomplicated bite-associated cellulitis. 4
Alternative Regimens
For Penicillin-Allergic Patients
- Doxycycline 100 mg twice daily provides excellent activity against P. multocida but requires combination with metronidazole for anaerobic coverage 1
- Moxifloxacin 400 mg daily offers monotherapy with good anaerobic coverage 1
- Trimethoprim-sulfamethoxazole 160-800 mg twice daily PLUS metronidazole 250-500 mg three times daily covers aerobes and anaerobes respectively 1
For Severe Infections Requiring IV Therapy
Ampicillin-sulbactam 1.5-3.0 g IV every 6-8 hours is the preferred intravenous option for hospitalized patients with severe bite-associated cellulitis. 1 Alternative IV regimens include:
Critical Pitfalls to Avoid
Do not use clindamycin as monotherapy for animal bite cellulitis—it has good activity against staphylococci, streptococci, and anaerobes but misses P. multocida, the most common pathogen in cat bites. 1
Do not use first-generation cephalosporins (cephalexin, cefazolin) alone—they provide good staphylococcal and streptococcal coverage but miss P. multocida and anaerobes. 1
Do not use trimethoprim-sulfamethoxazole as monotherapy—it has good aerobic activity but poor anaerobic coverage. 1
Special Considerations for High-Risk Bites
Preemptive antimicrobial therapy for 3-5 days is strongly recommended for patients with: 1
- Immunocompromise or asplenia 1
- Advanced liver disease 1
- Preexisting or resultant edema of the affected area 1
- Moderate to severe injuries, especially to the hand or face 1
- Injuries that may have penetrated the periosteum or joint capsule 1
Pathogen-Specific Evidence
Pasteurella multocida causes rapidly developing cellulitis within 12-24 hours of cat or dog bites, presenting with acute onset of lymphangitis and serosanguineous or purulent drainage. 2 This organism responds well to penicillins, with penicillin historically considered the drug of choice (MIC90 ≤0.06 μg/mL). 3 However, the polymicrobial nature of bite wounds—including anaerobes from animal oral flora—makes amoxicillin-clavulanate superior to penicillin alone. 1
When MRSA Coverage Is Needed
Add MRSA-active antibiotics only when specific risk factors are present: 4
- Penetrating trauma with purulent drainage 4
- Known MRSA colonization 4
- Injection drug use 4
- Systemic inflammatory response syndrome (SIRS) 4
In these cases, use clindamycin 300-450 mg three times daily (covers streptococci and MRSA) or trimethoprim-sulfamethoxazole plus a beta-lactam. 4 Note that amoxicillin-clavulanate lacks MRSA activity. 4
Adjunctive Measures
Elevate the affected extremity to promote drainage and hasten improvement. 4 Ensure tetanus prophylaxis is current and consult local health officials regarding rabies postexposure prophylaxis, which may be indicated depending on the animal and circumstances. 1