What is the empirical antibiotic therapy for a visible subcutaneous nodule in the axilla (armpit) approximately the size of a nickel?

Management of a Subcutaneous Nodule in the Axilla

For a subcutaneous nodule in the axilla approximately the size of a nickel, the empirical antibiotic therapy should include coverage for both Staphylococcus aureus (including MRSA) and streptococci, with amoxicillin-clavulanate being the first-line treatment option.

Evaluation and Diagnosis

• The axillary nodule is likely an abscess, which is a common skin and soft tissue infection
• Key considerations for assessment:
  • Size and characteristics of the nodule (nickel-sized, visible through skin)
  • Presence of systemic signs of infection (fever, tachycardia)
  • Extent of surrounding cellulitis
  • Patient's immune status and comorbidities

Treatment Algorithm

Step 1: Surgical Management

• Incision and drainage is the cornerstone of treatment for all abscesses 1
• Complete drainage should be performed to evacuate all purulent material

Step 2: Empiric Antibiotic Selection

For Uncomplicated Abscess (minimal surrounding cellulitis, no systemic signs):

• Incision and drainage alone may be sufficient 2
• However, axillary location warrants antibiotic coverage due to higher incidence of gram-negative organisms 3

For Abscess with Surrounding Cellulitis or Systemic Signs:

• First-line therapy: Amoxicillin-clavulanate 4

  • Provides coverage for:
    • Beta-lactamase-producing S. aureus
    • Streptococcal species
    • Gram-negative organisms common in axillary region
  • Dosing: 875/125 mg PO twice daily for 5-10 days

• Alternative options if MRSA is highly suspected:

  • Trimethoprim-sulfamethoxazole (1-2 DS tablets PO BID) 1
    • Note: Limited activity against streptococci
  • Clindamycin (300-450 mg PO TID) 1
    • Covers MRSA, streptococci, and anaerobes
    • Higher risk of C. difficile colitis
  • Doxycycline (100 mg PO BID) 1
    • Limited activity against streptococci

Rationale for Recommendation

1. Microbiology considerations:

   • Axillary abscesses commonly involve mixed flora including:
     • Staphylococcus aureus (including MRSA)
     • Streptococcal species
     • Gram-negative organisms 3

2. Evidence supporting amoxicillin-clavulanate:

   • FDA-approved for skin and skin structure infections caused by beta-lactamase-producing S. aureus, E. coli, and Klebsiella species 4
   • Effective against mixed streptococcal-staphylococcal infections 5
   • Provides coverage for the common pathogens in axillary infections

3. Special considerations for axillary location:

   • "Incisions in the axilla have a significant recovery of gram-negative organisms" 3
   • This anatomical location requires broader coverage than simple abscesses elsewhere

Important Caveats

• Obtain culture during drainage to guide definitive therapy 1

• Adjust antibiotics based on culture results and clinical response

• Consider MRSA coverage if:

  • High local prevalence of MRSA
  • Previous MRSA infection
  • Failure to respond to initial therapy

• For severe infections with systemic toxicity, consider broader coverage with vancomycin plus piperacillin-tazobactam or a carbapenem 1

• Rifampin should not be used as monotherapy due to rapid development of resistance 1

• Monitor for treatment failure, which may require reassessment and possibly imaging to rule out deeper infection

The IDSA guidelines emphasize that while incision and drainage is the primary treatment for abscesses, the anatomical location in the axilla and the size of the nodule warrant empiric antibiotic therapy with coverage for the common pathogens found in this region 3.