Is cloxacillin (dicloxacillin) superior to amoxicillin (amoxicillin) for treating animal bites?

Cloxacillin (Dicloxacillin) is NOT Superior to Amoxicillin for Animal Bites

Cloxacillin/dicloxacillin should NOT be used as monotherapy for animal bites because it has poor activity against Pasteurella multocida, the predominant pathogen in these infections, and should be avoided. 1

First-Line Treatment Recommendation

Amoxicillin-clavulanate is the recommended first-line antibiotic for animal bite wounds due to its broad coverage of the polymicrobial flora typically found in these infections. 1, 2

• This agent provides coverage against Pasteurella species (found in 50% of dog bites and 75% of cat bites), Staphylococcus aureus, Streptococcus species, and anaerobic bacteria. 1, 3
• Dosing: 500-875 mg orally twice daily for outpatient treatment. 1
• Duration: 7-14 days depending on severity, or 3-5 days for prophylaxis in high-risk wounds. 1, 3

Why Dicloxacillin Fails as Monotherapy

Dicloxacillin and other penicillinase-resistant penicillins have poor in vitro activity against Pasteurella multocida and should be avoided. 1

• Pasteurella species are isolated from 50% of dog bite wounds and 75% of cat bite wounds, making coverage essential. 1, 3
• First-generation cephalosporins (like cephalexin), penicillinase-resistant penicillins (dicloxacillin), macrolides, and clindamycin all miss Pasteurella coverage. 1
• Using antibiotics with inadequate Pasteurella coverage leads to treatment failure. 3

When Dicloxacillin Can Be Used

Dicloxacillin may be combined with penicillin VK as an alternative regimen, but this is inferior to amoxicillin-clavulanate. 1

• Combination dosing: Penicillin VK 500 mg four times daily PLUS dicloxacillin 500 mg four times daily. 1
• This combination provides coverage for both Pasteurella (via penicillin) and staphylococci (via dicloxacillin). 1
• However, this requires taking 8 pills daily versus 2 pills with amoxicillin-clavulanate, making compliance more challenging.

Alternative Regimens

If amoxicillin-clavulanate cannot be used:

• Doxycycline 100 mg twice daily has excellent activity against Pasteurella multocida, though some streptococci may be resistant. 1
• Fluoroquinolones (ciprofloxacin, levofloxacin, moxifloxacin) plus metronidazole or clindamycin for anaerobic coverage. 1
• These alternatives require adding a second agent for complete coverage, unlike amoxicillin-clavulanate which covers all pathogens as monotherapy. 1

Critical Clinical Pitfalls

Failure to recognize the polymicrobial nature of animal bite infections leads to inadequate treatment. 3

• Animal bite wounds yield an average of 5 different bacterial species, with 60% containing mixed aerobic and anaerobic bacteria. 1, 3
• Cat bites have higher infection rates (30-50%) compared to dog bites (5-25%) and greater prevalence of anaerobes (65% vs 50%). 1
• Hand wounds carry the highest risk of complications and require aggressive treatment. 1, 3

Intravenous Options for Severe Infections

For hospitalized patients or severe infections:

• Ampicillin-sulbactam 1.5-3.0 g every 6-8 hours. 1
• Piperacillin-tazobactam 3.37 g every 6-8 hours. 1
• Second-generation cephalosporins (cefoxitin) or carbapenems (ertapenem, imipenem, meropenem). 1