What is the most appropriate management of a purulent skin infection?

Management of Purulent Skin Infections

Incision and drainage is the primary and essential treatment for purulent skin infections (abscesses), with adjunctive antibiotics reserved for specific indications including systemic signs of infection, surrounding cellulitis >2 cm, immunocompromised status, or failure of drainage alone. 1

Primary Treatment: Incision and Drainage

• I&D is the cornerstone of therapy and must be performed for all abscesses - antibiotics alone are insufficient and will fail without adequate drainage 1, 2
• Ensure complete evacuation of purulent material using multiple counter incisions for large abscesses rather than a single long incision to prevent step-off deformity and delayed healing 1
• Obtain purulent material for Gram stain and culture before initiating antibiotics to identify pathogens and guide targeted therapy 2, 3

Indications for Adding Antibiotics After I&D

Antibiotics should be added when any of the following are present:

• Systemic inflammatory response syndrome (SIRS) criteria: fever >38°C or <36°C, heart rate >90 bpm, respiratory rate >24 breaths/min, or WBC >12,000 or <4,000 cells/μL 1, 3
• Surrounding cellulitis or erythema extending >2 cm beyond the abscess margin 1, 4
• Multiple sites of infection 4
• Immunocompromised status, diabetes, or other significant comorbidities 1
• Failure of initial I&D or inadequate source control 3
• Abscess in high-risk anatomic locations (face, hands, genitalia) 3

For simple abscesses <5 cm without these features, I&D alone is sufficient 1, 4

Antibiotic Selection When Indicated

Empiric Coverage for Community-Acquired MRSA

Since MRSA causes approximately 50% of purulent skin infections in the United States, empiric therapy must cover this pathogen when antibiotics are warranted 4, 5

Oral options for outpatients (systemically well):

• Clindamycin 300-450 mg three times daily - covers both MRSA and streptococci, preferred first-line agent 1, 3, 4
• Trimethoprim-sulfamethoxazole (TMP-SMX) 1-2 double-strength tablets twice daily - covers MRSA but lacks streptococcal activity; should NOT be used as monotherapy when streptococcal infection is possible 1, 3
• Doxycycline 100 mg twice daily - covers MRSA, alternative option 1, 3

Intravenous options for hospitalized patients with systemic signs:

• Vancomycin 15-20 mg/kg IV every 8-12 hours - indicated for patients meeting SIRS criteria or requiring hospitalization 1, 3, 6

Important Nuance on Antibiotic Choice

The 2017 placebo-controlled trial demonstrated that both clindamycin and TMP-SMX improved cure rates compared to I&D alone (83.1% and 81.7% vs 68.9%, p<0.001), but clindamycin resulted in fewer new infections at 1 month (6.8% vs 13.5%, p=0.03) 4. However, clindamycin had higher adverse event rates (21.9% vs 11.1%) 4. This benefit was restricted to patients with confirmed S. aureus infection 4.

Duration of Antibiotic Therapy

• 5-10 days of therapy is recommended based on clinical response 1, 2, 7
• Adjust duration based on improvement; extend if infection has not improved within 5 days 2
• Shorter courses (5-7 days) are typically adequate to achieve cure 7

Follow-Up and Monitoring

• Re-evaluate within 48-72 hours to assess response to treatment and ensure adequate drainage 2, 3
• Adjust antibiotics based on culture results and clinical response 2
• If no improvement or worsening occurs, consider inadequate drainage, resistant organisms, or deeper extension of infection 3

Critical Pitfalls to Avoid

Failure to Perform Adequate Drainage

• The most common error is relying on antibiotics without I&D - drainage is essential and antibiotics alone will fail 2, 3
• Inadequate drainage leads to treatment failure; ensure complete evacuation of all purulent material 2

Inappropriate Antibiotic Use

• Do not routinely prescribe antibiotics for simple abscesses after adequate I&D - this contributes to antibiotic resistance without improving outcomes 3
• Avoid using TMP-SMX as sole therapy when streptococcal infection is possible due to lack of streptococcal coverage 3
• Do not use cephalexin or other beta-lactams for suspected MRSA infections 8

Premature Discontinuation

• Insufficient duration of treatment can lead to recurrence; continue antibiotics until clinical improvement is evident 2

Delayed Culture Collection

• Always obtain specimens before initiating antimicrobial therapy to guide targeted treatment 2, 3

Special Considerations

Complicated Infections Requiring Broad-Spectrum Coverage

For patients with systemic toxicity, severe comorbidities, or complicated infections (Class 3-4 severity), initiate broad-spectrum antibiotics covering aerobic and anaerobic organisms, with consideration for MRSA coverage 1

Blood Cultures

Obtain blood cultures in patients with high fever, hypotension, malignancy, neutropenia, severe immunodeficiency, or other severe systemic features 1, 2