In an adult with normal renal function and no β‑lactam allergy who has cellulitis from a dog bite, does amoxicillin‑clavulanate (Augmentin) cover all the organisms that cephalexin would treat?

Does Augmentin Cover All the Organisms That Cephalexin Would in Dog Bite Cellulitis?

Yes, amoxicillin-clavulanate (Augmentin) covers all the organisms that cephalexin would treat in cellulitis, PLUS it provides essential coverage against Pasteurella multocida and anaerobes that cephalexin misses—making Augmentin superior and the recommended first-line agent for dog bite infections. 1

Why Cephalexin Is Inadequate for Dog Bites

First-generation cephalosporins like cephalexin have poor in vitro activity against Pasteurella multocida and should be avoided in animal bite wounds. 1 This is a critical distinction because:

• Pasteurella species are isolated from 50% of dog bite wounds and 75% of cat bite wounds 1
• Cephalexin provides excellent coverage against streptococci and methicillin-sensitive Staphylococcus aureus (the typical cellulitis pathogens) 2, 3
• However, dog bites yield an average of 5 types of bacterial isolates (range 0-16), with ~60% yielding mixed aerobic and anaerobic bacteria 1
• Anaerobes commonly isolated include Bacteroides species, fusobacteria, Porphyromonas species, Prevotella heparinolytica, proprionibacteria, and peptostreptococci 1

What Augmentin Covers That Cephalexin Does Not

Amoxicillin-clavulanate provides single-agent coverage for the polymicrobial oral flora of dogs, including:

• All organisms cephalexin covers: streptococci and MSSA 1, 4
• Pasteurella multocida (present in 50% of dog bites) 1
• Anaerobic bacteria (present in 50-65% of bite wounds) 1
• Beta-lactamase-producing organisms through the clavulanate component 1, 4

Evidence-Based Recommendation

The IDSA guidelines explicitly recommend amoxicillin-clavulanate 875/125 mg twice daily as first-line oral therapy for dog bite wounds (B-II evidence). 1 This recommendation is based on:

• Small case series demonstrating efficacy 1
• The polymicrobial nature of bite wounds requiring broad-spectrum coverage 1
• The high prevalence of Pasteurella species that cephalexin misses 1

Alternative Regimens (When Augmentin Cannot Be Used)

If amoxicillin-clavulanate is contraindicated, acceptable alternatives include:

• Doxycycline 100 mg twice daily (excellent activity against P. multocida, though some streptococci are resistant) 1
• Penicillin VK 500 mg four times daily PLUS dicloxacillin 500 mg four times daily 1
• Fluoroquinolones (ciprofloxacin, levofloxacin, moxifloxacin) PLUS metronidazole or clindamycin for anaerobic coverage 1

Critical Pitfalls to Avoid

• Never use cephalexin alone for dog bite cellulitis—it misses Pasteurella and anaerobes that are present in the majority of cases 1
• Do not use macrolides (erythromycin) or clindamycin alone—both have poor activity against P. multocida 1
• Avoid penicillinase-resistant penicillins (dicloxacillin) as monotherapy—they also miss Pasteurella 1

Treatment Duration and Adjunctive Measures

• Treat for 3-5 days for preemptive early therapy in high-risk wounds (hand/face injuries, deep punctures, immunocompromised patients) 1
• Cleanse wounds with sterile normal saline—no need for iodine or antibiotic-containing solutions 1
• Elevate the injured body part during the first few days after injury to accelerate healing 1
• Assess for rabies prophylaxis in consultation with local health officials 1

When to Escalate to IV Therapy

For severe bite infections requiring hospitalization, use:

• Ampicillin-sulbactam 1.5-3.0 g IV every 6-8 hours 1
• Piperacillin-tazobactam 3.37 g IV every 6-8 hours 1
• Carbapenems (ertapenem, imipenem, meropenem) 1

All IV regimens provide the same broad polymicrobial coverage as oral Augmentin but are reserved for severe infections, systemic toxicity, or complications like osteomyelitis (requiring 4-6 weeks) or septic arthritis (requiring 3-4 weeks). 1