How should a 65-year-old man with a worsening carbuncle on the left upper back, foul-smelling purulent drainage after incision and drainage, and currently on amoxicillin-clavulanate (augmentin) be managed?

Management of Carbuncle with Dermatome-like Erythema After I&D

Continue augmentin (amoxicillin-clavulanate) as empiric therapy, but immediately add MRSA coverage with either doxycycline, clindamycin, or trimethoprim-sulfamethoxazole (TMP-SMX) given the concerning dermatome-like erythema and foul-smelling purulent drainage, and adjust based on culture results. 1

Key Clinical Concerns

The dermatome-like erythema extending laterally below the carbuncle is particularly concerning and suggests:

• Extensive cellulitis beyond the abscess cavity
• Possible necrotizing infection (though less likely given the description)
• Polymicrobial infection requiring broader coverage

The foul-smelling purulent drainage with thick white caseous material indicates likely polymicrobial infection involving anaerobes, which augmentin does cover, but the extensive cellulitis mandates additional MRSA coverage.

Antibiotic Management Algorithm

Current augmentin is appropriate for anaerobic coverage 1, but requires augmentation:

Add MRSA Coverage Immediately:

• Doxycycline 100 mg PO BID (preferred for excellent tissue penetration) 1
• OR Clindamycin 300 mg PO TID (good for both MRSA and anaerobes) 1
• OR TMP-SMX 160-800 mg PO BID (note: poor anaerobic coverage, so keep augmentin) 1

Duration:

• Continue dual therapy for 7 days minimum 1
• Reassess at 48-72 hours for clinical improvement
• If no improvement by 48-72 hours, consider IV therapy and imaging to rule out deeper infection

Rationale for Dual Therapy

The IDSA guidelines specifically recommend that adjunctive antibiotics for carbuncles and abscesses should be considered when there is significant surrounding cellulitis 1. Your patient has:

1. Extensive dermatome-like erythema (significant cellulitis)
2. Large carbuncle (3x4 cm)
3. Foul-smelling drainage suggesting polymicrobial infection
4. Age 65 with potential comorbidities

Augmentin alone misses MRSA 1, which is a critical pathogen in carbuncles and skin abscesses. The guidelines explicitly note this limitation in their treatment tables 1.

Wound Care

• Continue iodoform packing changes daily until drainage resolves 1
• Monitor for signs of necrotizing infection: crepitus, rapid progression, systemic toxicity, skin necrosis
• Consider removing packing and transitioning to simple dressing once drainage decreases (typically 3-5 days)

Red Flags Requiring Immediate Escalation

Return immediately or admit if:

• Fever >38.5°C or systemic signs of sepsis
• Rapid extension of erythema despite antibiotics
• Development of skin necrosis, bullae, or crepitus
• Worsening pain out of proportion to exam
• Failure to improve within 48-72 hours

These would indicate possible necrotizing fasciitis or deeper space infection requiring IV antibiotics, surgical debridement, and possible imaging (CT or MRI).

Culture Follow-up

Adjust antibiotics based on culture results 1:

• If MSSA grows: can discontinue MRSA coverage, continue augmentin alone
• If MRSA confirmed: discontinue augmentin, continue MRSA-active agent alone (unless anaerobes also isolated)
• If polymicrobial with anaerobes: continue dual therapy as prescribed

Common Pitfalls to Avoid

1. Do not rely on augmentin monotherapy when significant cellulitis is present—it misses MRSA 1
2. Do not use TMP-SMX alone—it has poor anaerobic coverage and the foul smell indicates anaerobes 1
3. Do not delay adding MRSA coverage until culture results return—empiric coverage is critical given the extent of cellulitis 1
4. Do not forget tetanus prophylaxis if not up to date within 10 years 1