What's the next step for a patient with a boil under the armpit who is not improving on Bactrim (trimethoprim/sulfamethoxazole) after 2 days?

Management of Axillary Boil Not Responding to Bactrim After 2 Days

For a patient with a boil under the armpit not improving after 2 days of Bactrim (trimethoprim/sulfamethoxazole), incision and drainage of the abscess is the recommended next step, followed by changing antibiotic therapy if necessary.

Assessment of Treatment Failure

When a patient with a cutaneous abscess fails to improve after 48-72 hours of initial antibiotic therapy, this meets criteria for treatment failure according to multiple guidelines:

• Guidelines recommend reassessment if symptoms worsen after 48-72 hours of initial empiric antimicrobial therapy or fail to improve despite 3-5 days of treatment 1
• Treatment failure should prompt reevaluation of the diagnosis, exclusion of other causes, and detection of complications 1

Next Steps in Management

1. Incision and Drainage (I&D)

• The primary intervention for a boil/abscess that is not responding to antibiotics is incision and drainage
• I&D is the definitive treatment for cutaneous abscesses regardless of antibiotic therapy
• This procedure allows for:
  • Direct removal of purulent material
  • Decompression of the abscess cavity
  • Collection of material for culture and susceptibility testing

2. Culture and Susceptibility Testing

• Obtain cultures from the drained abscess material to identify the causative organism and its antibiotic susceptibility pattern
• This is particularly important when initial empiric therapy has failed
• Direct cultures from the abscess are more reliable than surface swabs 1

3. Antibiotic Modification

After I&D, antibiotic therapy should be modified based on the following considerations:

• Change to a different antibiotic class: Since Bactrim has failed, consider:

  • Clindamycin (if MRSA is suspected)
  • Doxycycline
  • Linezolid (for severe cases with multidrug-resistant organisms)

• Duration of therapy: Continue the new antibiotic regimen for 7-10 days

Guidelines specifically note that when treatment failure is observed after antibiotic therapy, "infection with drug-resistant bacteria should be considered and should prompt a switch to alternate antibiotic therapy" 1

Rationale for Changing Antibiotics

Although trimethoprim-sulfamethoxazole (Bactrim) is often effective against community-acquired MRSA skin infections 2, treatment failure may occur due to:

1. Resistant organisms: The causative bacteria may be resistant to Bactrim
2. Inadequate drainage: An undrained abscess may not respond to antibiotics alone
3. Alternative pathogens: The infection may be caused by organisms not covered by Bactrim

Special Considerations

• Location matters: Axillary abscesses can be particularly problematic due to the warm, moist environment and proximity to lymph nodes
• Recurrent infections: If this is a recurrent issue, consider underlying conditions such as hidradenitis suppurativa or immunodeficiency
• Systemic symptoms: If the patient has fever, chills, or other signs of systemic infection, more aggressive management may be needed

Common Pitfalls to Avoid

1. Delaying drainage: Continuing antibiotics without drainage when an abscess is present
2. Inadequate follow-up: Failing to reassess within 48-72 hours after changing therapy
3. Incomplete drainage: Not breaking all loculations within the abscess cavity
4. Overlooking resistance: Not considering antibiotic resistance when initial therapy fails

Algorithm for Management

1. Perform I&D of the axillary abscess
2. Obtain cultures from the abscess material
3. Change antibiotic therapy to an alternative agent with different mechanism of action
4. Follow up within 48-72 hours to assess response to the new treatment
5. Adjust therapy based on culture results when available

This approach aligns with guidelines that recommend reassessment and change in management strategy when initial therapy fails after 48-72 hours 1.