What is the preferred co-antibiotic, doxycycline or clindamycin, to use with co-amoxiclav (amoxicillin/clavulanate) for treating animal bites?

Antibiotic Co-Therapy for Animal Bites with Co-Amoxiclav

Direct Answer

Neither doxycycline nor clindamycin should be routinely added to co-amoxiclav (amoxicillin-clavulanate) for animal bite infections, as amoxicillin-clavulanate alone provides complete coverage as first-line monotherapy. 1, 2

Why Amoxicillin-Clavulanate is Sufficient as Monotherapy

• Amoxicillin-clavulanate covers the entire polymicrobial spectrum of animal bite pathogens including Pasteurella multocida (present in 50% of dog bites and 75% of cat bites), Staphylococcus aureus, streptococci, and anaerobes (Bacteroides, Fusobacterium, Porphyromonas species). 1, 2, 3

• Animal bite wounds contain an average of 5 different bacterial species, with 60% harboring mixed aerobic and anaerobic bacteria, making broad-spectrum monotherapy the optimal approach rather than combination therapy. 2, 3

• The IDSA 2014 guidelines list amoxicillin-clavulanate 875/125 mg twice daily as the sole oral first-line agent for animal bites, with no recommendation for adding co-antibiotics. 1

When Co-Antibiotics Are Actually Indicated

Doxycycline Should Be Used Instead (Not Added) When:

• Penicillin allergy exists: Doxycycline 100 mg twice daily provides excellent activity against Pasteurella multocida but has poor coverage of some streptococci and no anaerobic coverage. 1, 2

• Doxycycline must be combined with metronidazole or clindamycin when used as an alternative regimen to cover anaerobes adequately. 1

Clindamycin Should Be Used Instead (Not Added) When:

• Clindamycin 300 mg three times daily has good activity against staphylococci, streptococci, and anaerobes but critically misses Pasteurella multocida, making it inadequate as monotherapy. 1

• If clindamycin is chosen (e.g., for severe penicillin allergy), it must be combined with a fluoroquinolone (ciprofloxacin or levofloxacin) to cover Pasteurella species. 1

Critical Clinical Pitfalls to Avoid

• Do not add doxycycline or clindamycin to amoxicillin-clavulanate as this provides no additional benefit and increases cost, side effects, and antibiotic resistance pressure. 1, 2

• Cat bites have higher infection rates (30-50%) versus dog bites (5-25%) and greater anaerobic prevalence (65% vs 50%), but this does not change the first-line antibiotic choice—amoxicillin-clavulanate remains appropriate. 2

• Dicloxacillin and other penicillinase-resistant penicillins fail as monotherapy due to poor activity against Pasteurella multocida and should never be used alone for animal bites. 2

Appropriate Alternative Regimens (Replacement, Not Addition)

For penicillin-allergic patients:

• Doxycycline 100 mg twice daily PLUS metronidazole 500 mg three times daily provides coverage of Pasteurella and anaerobes. 1

• Fluoroquinolone (levofloxacin 750 mg daily or moxifloxacin 400 mg daily) PLUS metronidazole or clindamycin for anaerobic coverage. 1

• Trimethoprim-sulfamethoxazole 160-800 mg twice daily has good aerobic activity but poor anaerobic coverage, requiring metronidazole addition. 1

Severe Infections Requiring Intravenous Therapy

• Ampicillin-sulbactam 1.5-3.0 g every 6-8 hours or piperacillin-tazobactam 3.37 g every 6-8 hours for hospitalized patients with severe infections. 1, 2

• Second- and third-generation cephalosporins (cefuroxime, ceftriaxone, cefotaxime) provide good Pasteurella coverage but miss anaerobes and require metronidazole addition. 1

Treatment Duration

• 7-14 days for established infections depending on severity. 2

• 3-5 days for prophylaxis in high-risk wounds (deep punctures, hand injuries, immunocompromised patients, presentation >12 hours after injury). 2