What is the best antibiotic for treating cellulitis (inflammation of the skin and subcutaneous tissues) following a dog bite?

Best Antibiotic for Cellulitis After Dog Bite

Amoxicillin-clavulanate is the first-line antibiotic of choice for treating cellulitis following a dog bite. 1 This combination provides coverage against both aerobic and anaerobic bacteria commonly found in dog bite wounds, including the critical pathogen Pasteurella multocida.

Microbiology of Dog Bite Wounds

Dog bite wounds have a complex polymicrobial nature:

• Aerobic bacteria:

  • Pasteurella multocida (found in 50% of dog bite wounds) 1
  • Staphylococci and streptococci (found in ~40% of bites) 1
  • Capnocytophaga canimorsus (particularly dangerous in immunocompromised patients) 1
  • Eikenella corrodens

• Anaerobic bacteria:

  • Bacteroides species
  • Fusobacteria
  • Porphyromonas species
  • Prevotella species
  • Peptostreptococci 1

Treatment Recommendations

First-line Therapy:

• Oral: Amoxicillin-clavulanate 875/125 mg twice daily 1
• Intravenous (for severe infections): Ampicillin-sulbactam 1.5-3.0 g every 6-8 hours 1

Alternative Options (for penicillin-allergic patients):

• Doxycycline 100 mg twice daily (excellent activity against P. multocida) 1
• Moxifloxacin 400 mg daily (good for both aerobes and anaerobes) 1
• Combination therapy: Trimethoprim-sulfamethoxazole (for aerobes) plus metronidazole (for anaerobes) 1

Important Clinical Considerations

Duration of Therapy:

• For uncomplicated cellulitis: 5 days of antibiotic treatment is as effective as a 10-day course 2
• For complications (osteomyelitis, septic arthritis): 4-6 weeks for osteomyelitis, 3-4 weeks for synovitis 1

Medications to Avoid:

• First-generation cephalosporins (cephalexin)
• Penicillinase-resistant penicillins (dicloxacillin)
• Macrolides (erythromycin)
• Clindamycin alone (misses P. multocida) 1

These medications have poor activity against P. multocida, which is a key pathogen in dog bite wounds 1.

Adjunctive Measures:

• Wound cleansing with sterile normal saline
• Elevation of the affected area to reduce edema
• Tetanus prophylaxis if not vaccinated within 10 years (Tdap preferred if not previously given) 1
• Rabies post-exposure prophylaxis may be indicated (consult local health officials) 1

Special Considerations

High-Risk Patients:

Preemptive early antimicrobial therapy for 3-5 days is strongly recommended for patients who:

• Are immunocompromised
• Are asplenic
• Have advanced liver disease
• Have preexisting or resultant edema of the affected area
• Have moderate to severe injuries, especially to the hand or face
• Have injuries that may have penetrated the periosteum or joint capsule 1

Monitoring and Follow-up:

• Follow up within 24 hours either by phone or office visit
• Consider hospitalization if infection progresses despite appropriate antimicrobial therapy 1
• Watch for complications such as septic arthritis, osteomyelitis, abscess formation, tendonitis, and bacteremia 1

Pharmacological Rationale

Amoxicillin-clavulanate combines amoxicillin (a semisynthetic antibiotic with bactericidal activity against Gram-positive and Gram-negative bacteria) with clavulanic acid (a beta-lactamase inhibitor). This combination protects amoxicillin from degradation by beta-lactamases commonly found in resistant microorganisms, extending its spectrum to include many bacteria normally resistant to amoxicillin alone 3.

The formulation has demonstrated in vitro activity against key pathogens in dog bite wounds, including Staphylococcus aureus, Pasteurella multocida, Eikenella corrodens, Bacteroides species, Fusobacterium species, and Peptostreptococcus species 3, 4.