What antibiotic regimen is recommended for a dog bite?

Dog Bite Antibiotic Management

For dog bite wounds, amoxicillin-clavulanate is the first-line antibiotic for both prophylaxis and treatment, given its proven efficacy against the polymicrobial flora typical of these injuries, including Pasteurella multocida, staphylococci, streptococci, and anaerobes. 1

Antibiotic Selection

First-Line Therapy

• Amoxicillin-clavulanate is the recommended oral agent, studied specifically for dog and cat bites and provides coverage against the mixed aerobic-anaerobic flora 1
• Standard adult dosing: 875 mg/125 mg every 12 hours for more severe infections, or 500 mg/125 mg every 12 hours for less severe wounds 2
• Pediatric dosing (≥12 weeks): 45 mg/kg/day divided every 12 hours for more severe infections, or 25 mg/kg/day every 12 hours for less severe infections 2

Alternative Oral Regimens (if amoxicillin-clavulanate unavailable or contraindicated)

• Doxycycline 100 mg twice daily 1, 3
• Penicillin VK plus dicloxacillin combination 1
• Fluoroquinolones (ciprofloxacin, levofloxacin, moxifloxacin) PLUS metronidazole or clindamycin for anaerobic coverage 1
• Trimethoprim-sulfamethoxazole PLUS metronidazole or clindamycin 1

Antibiotics to AVOID

• First-generation cephalosporins (e.g., cephalexin) have poor activity against Pasteurella multocida 1
• Penicillinase-resistant penicillins (e.g., dicloxacillin alone) lack coverage for Pasteurella 1
• Macrolides (e.g., erythromycin) are inadequate against Pasteurella 1
• Clindamycin alone lacks Pasteurella coverage 1

Intravenous Options (for severe infections requiring hospitalization)

• Ampicillin-sulbactam 1
• Piperacillin-tazobactam 1
• Second-generation cephalosporins (e.g., cefoxitin) 1
• Carbapenems (ertapenem, imipenem, meropenem) 1

Microbiology of Dog Bites

Understanding the bacterial flora guides antibiotic selection:

• Dog bite wounds yield an average of 5 bacterial species (range 0-16), with approximately 60% containing mixed aerobic-anaerobic bacteria 1
• Pasteurella species are isolated from 50% of dog bite wounds 1
• Staphylococci and streptococci are found in approximately 40% of dog bites 1
• Anaerobes (Bacteroides, Fusobacteria, Porphyromonas, Prevotella, Peptostreptococci) are present in 50% of cases 1
• Capnocytophaga canimorsus can cause fatal sepsis, particularly in asplenic or immunocompromised patients 1

Indications for Antibiotic Prophylaxis

Prophylactic antibiotics reduce infection rates from 16% to approximately 9%, with a number needed to treat of 14 patients to prevent one infection. 4

High-Risk Wounds Requiring Prophylaxis:

• Puncture wounds (deeper penetration with higher infection risk) 5, 6
• Hand wounds (increased risk of serious complications including tenosynovitis and osteomyelitis) 1, 5, 6
• Wounds requiring closure 5, 6
• Immunocompromised patients 5, 6
• Wounds presenting >8-12 hours after injury (higher baseline infection risk) 1
• Wounds near bones or joints (risk of osteomyelitis or septic arthritis) 1

Consider Prophylaxis for All Dog Bites

Given the meta-analysis showing benefit and the polymicrobial nature of these wounds, antibiotic prophylaxis should be strongly considered for all dog bites, particularly those meeting high-risk criteria 6, 4

Essential Wound Management

Antibiotics are adjunctive to proper wound care:

• Immediate copious irrigation with normal saline using a 20-mL or larger syringe (or 20-gauge catheter attached) to generate adequate pressure 5, 6
• Thorough cleansing with soap and water markedly reduces infection risk and rabies transmission 1
• Povidone-iodine solution irrigation further decreases bacterial infection risk 1
• Debridement of devitalized tissue and removal of foreign bodies 5, 6
• Avoid suturing when possible; infected wounds should never be closed 1
• Facial wounds may be closed primarily after meticulous wound care due to cosmetic considerations and lower infection risk 1

Tetanus Prophylaxis

• Tetanus immunization status must be assessed for all bite wounds 1
• Administer tetanus toxoid (0.5 mL intramuscularly) if vaccination status is outdated or unknown 1

Rabies Considerations

• Healthy domestic dogs may be confined and observed for 10 days rather than immediate euthanasia 1
• Unprovoked attacks are more likely to indicate rabies risk 1
• Currently vaccinated dogs are unlikely to transmit rabies 1
• If rabies exposure is suspected in previously unvaccinated persons, administer both rabies immune globulin (20 IU/kg) and vaccine on days 0,3,7,14, and 28 1

Duration of Therapy

• Uncomplicated wounds: 3-5 days of prophylactic antibiotics 5, 6
• Established infections: 7-10 days or until clinical resolution 5, 6
• Osteomyelitis: 4-6 weeks 1
• Septic arthritis: 3-4 weeks 1

Common Pitfalls

• Failing to recognize hand wounds as high-risk: Hand bites require aggressive management due to proximity to tendons, joints, and bones 1
• Using inadequate antibiotic coverage: Single agents without Pasteurella activity (cephalexin, dicloxacillin, clindamycin alone) lead to treatment failures 1
• Premature wound closure: Increases infection risk, particularly for puncture wounds and contaminated injuries 1
• Neglecting rabies assessment: Even domestic animals may be unvaccinated 5, 6