What is the recommended antibiotic regimen for an infected dog bite?

Antibiotic for Infected Dog Bite

For an infected dog bite, amoxicillin-clavulanate 875/125 mg twice daily orally is the first-line treatment, providing comprehensive coverage against the polymicrobial flora including Pasteurella species (present in 50% of dog bites), Staphylococcus aureus, streptococci, and anaerobes. 1, 2

Oral Antibiotic Options

First-line therapy:

• Amoxicillin-clavulanate 875/125 mg twice daily is the preferred oral agent, with documented efficacy in clinical trials and optimal coverage of the typical polymicrobial flora 1, 2, 3

Alternative oral regimens (for penicillin allergy or treatment failure):

• Doxycycline 100 mg twice daily provides excellent activity against Pasteurella multocida 1, 2
• Moxifloxacin as monotherapy offers comprehensive coverage without requiring additional anaerobic coverage 1, 2, 4
• Clindamycin plus a fluoroquinolone (ciprofloxacin or levofloxacin) provides dual coverage 1, 2

Avoid these agents as they have poor activity against Pasteurella multocida:

• First-generation cephalosporins (e.g., cephalexin) 1, 2
• Macrolides (e.g., erythromycin) 1
• Penicillinase-resistant penicillins alone (e.g., dicloxacillin) 1, 2

Intravenous Options for Severe Infections

When systemic symptoms, moderate-to-severe infection, or high-risk wounds (hand involvement, joint/bone penetration) are present, initiate IV therapy for 3-5 days before transitioning to oral 2:

• Ampicillin-sulbactam 1
• Piperacillin-tazobactam 1, 2
• Cefoxitin (second-generation cephalosporin) 1, 2
• Ceftriaxone plus metronidazole 2
• Carbapenems (ertapenem, imipenem, or meropenem) 1, 2

Treatment Duration Algorithm

Uncomplicated soft tissue infections:

• Total duration: 7-10 days 2
• Transition from IV to oral when the patient is afebrile, shows clinical improvement, and local signs of infection are resolving 2

Complicated infections requiring prolonged therapy:

• Septic arthritis: 3-4 weeks total 2
• Osteomyelitis: 4-6 weeks total 1, 2
• Hand wounds often require longer treatment due to higher complication rates 1, 2

Microbiology Considerations

Dog bite wounds contain an average of 5 different bacterial species, with 60% yielding mixed aerobic and anaerobic organisms 1:

• Pasteurella species: isolated from 50% of dog bite wounds 1, 2
• Staphylococcus aureus and streptococci: found in approximately 40% of cases 1, 2
• Anaerobes (Bacteroides, Fusobacterium, Porphyromonas, Prevotella): common pathogens 1, 2
• Capnocytophaga canimorsus: a critical pathogen causing bacteremia and fatal sepsis, particularly in asplenic patients or those with advanced liver disease 1, 2

High-Risk Features Requiring Aggressive Management

Patient factors:

• Immunocompromised status 2
• Advanced liver disease (risk for Capnocytophaga sepsis) 1, 2
• Asplenia (risk for Capnocytophaga sepsis) 1, 2
• Pre-existing or resultant edema of the affected area 2

Wound characteristics:

• Hand, foot, face, or genital location 2
• Injuries that may have penetrated periosteum or joint capsule 2
• Pain disproportionate to injury severity near bone or joint suggests periosteal penetration 1

Essential Adjunctive Management

• Thorough wound cleansing with copious sterile normal saline irrigation using a 20-mL or larger syringe 2, 5
• Debridement of necrotic tissue and exploration for foreign bodies 2
• Assessment for tendon, bone, or joint involvement 2, 5
• Tetanus prophylaxis if vaccination not current within 10 years 2
• Rabies prophylaxis consultation with local health officials; if indicated, administer immune globulin plus vaccination on days 0,3,7, and 14 2, 5

Critical Pitfalls to Avoid

• Never use monotherapy with agents lacking Pasteurella coverage (first-generation cephalosporins, macrolides, or penicillinase-resistant penicillins alone), as Pasteurella multocida is present in 50% of dog bites and these agents have poor activity against it 1, 2
• Consider Capnocytophaga canimorsus in asplenic or liver disease patients, as this organism causes fulminant sepsis in these populations 1, 2
• Hand wounds require heightened vigilance due to higher rates of serious complications including septic arthritis and osteomyelitis 1, 2
• If using fluoroquinolones (ciprofloxacin, levofloxacin) or TMP-SMX, add metronidazole or clindamycin for anaerobic coverage 1