A patient with a dog bite wound two weeks ago was treated with amoxicillin‑clavulanate (Augmentin) but still has persistent redness and inflammation after completing therapy; which oral antibiotic should be used for a second course to provide MRSA coverage and anaerobic activity?

Doxycycline 100 mg twice daily for 7-10 days is the recommended antibiotic for this treatment failure

For a dog bite wound that has failed two courses of antibiotics including amoxicillin-clavulanate and remains red and inflamed after 2 weeks, you should prescribe doxycycline 100 mg twice daily, as it provides excellent coverage against Pasteurella multocida (the most common dog bite pathogen) while also covering MRSA, which is likely the culprit in this persistent infection. 1

Why This Treatment Failed

The persistent inflammation after two antibiotic courses strongly suggests:

• MRSA colonization/infection - Amoxicillin-clavulanate explicitly misses MRSA coverage 1, and all MRSA isolates are resistant to amoxicillin-clavulanate 2
• Inadequate wound care - Irrigation and debridement are at least equally important as antibiotics 3
• Possible abscess formation requiring drainage

The Doxycycline Advantage

Doxycycline is specifically highlighted in IDSA guidelines for dog bites because it:

• Has excellent activity against Pasteurella multocida (the primary dog bite pathogen) 1
• Provides MRSA coverage that amoxicillin-clavulanate lacks 1
• Covers anaerobes adequately for bite wounds 1
• Is cost-effective compared to alternatives

The main caveat: Some streptococci are resistant to doxycycline 1, but given two failed courses of beta-lactams (which cover streptococci well), MRSA is the more likely culprit here.

Alternative Regimen if Doxycycline Fails

If the patient cannot tolerate doxycycline or it fails:

Moxifloxacin 400 mg daily provides:

• Monotherapy coverage of aerobes AND anaerobes 1
• Good activity against Pasteurella multocida 1
• Broader coverage than other fluoroquinolones

Or consider combination therapy:

• Trimethoprim-sulfamethoxazole (160-800 mg twice daily) PLUS metronidazole (500 mg three times daily) 1
  • TMP-SMX covers MRSA and aerobes but misses anaerobes
  • Metronidazole fills the anaerobic gap

Critical Action Items Beyond Antibiotics

1. Re-examine the wound immediately - Look for:

   • Purulent drainage suggesting abscess requiring incision and drainage
   • Tracking erythema suggesting deeper infection
   • Crepitus suggesting gas-forming organisms
   • Fluctuance requiring drainage

2. Aggressive wound irrigation if not already done - This is as important as antibiotics 3

3. Consider imaging if deep infection suspected (ultrasound for abscess, X-ray for foreign body/gas)

4. Culture the wound before starting new antibiotics - This should have been done after the first failure

5. Verify tetanus status - Should have been updated if >10 years 1

When to Hospitalize

Consider IV antibiotics and admission if:

• Systemic signs (fever, tachycardia, hypotension)
• Rapidly spreading cellulitis
• Hand involvement with functional impairment
• Immunocompromised host
• Failed outpatient oral therapy (which is your current situation)

IV options for admission: Ampicillin-sulbactam 1.5-3 g every 6 hours PLUS vancomycin for MRSA coverage, or piperacillin-tazobactam 3.37 g every 6-8 hours PLUS vancomycin 1

Duration of Therapy

• 7-10 days of doxycycline for established infection
• Longer courses (up to 14 days) if slow to respond
• Clinical improvement should be evident within 48-72 hours

The key error in this case was likely inadequate initial wound management and missing MRSA coverage from the start. The IDSA guidelines explicitly note that amoxicillin-clavulanate "misses MRSA" 1, making it a poor choice for treatment failures or high-risk wounds.