What is the best course of action for a patient with a partially drained abscess (partial incision and drainage), who has failed to respond to initial treatment with Keflex (cephalexin) and Clindamycin, and still has purulent drainage despite a negative initial culture?

Management of Treatment-Refractory Abscess with Negative Culture

Yes, obtain repeat cultures AND proceed with complete surgical drainage—inadequate drainage is the most common cause of treatment failure, and repeat cultures are essential to guide targeted antibiotic therapy when initial empiric coverage has failed. 1, 2, 3

Immediate Surgical Intervention

Complete incision and drainage is the cornerstone of abscess treatment and must be performed urgently. 1, 2

• Partial I&D is inadequate and directly correlates with treatment failure—your patient requires complete surgical exploration and evacuation of all purulent material. 1, 3
• The presence of ongoing purulent drainage after partial drainage indicates residual undrained collections or loculations that require definitive surgical management. 1, 2
• A study of complicated peri-rectal abscesses demonstrated that inadequate drainage resulted in a six-fold increase in readmission rates, emphasizing that surgical source control supersedes antibiotic selection. 3

Repeat Culture Strategy

Obtain repeat cultures from the abscess cavity during complete drainage to identify the causative organism and guide definitive antibiotic therapy. 1, 2

• Initial negative cultures may result from inadequate sampling, prior antibiotic exposure (you've already given Keflex and clindamycin), or fastidious organisms requiring special culture conditions. 2
• Send specimens for aerobic, anaerobic, and fungal cultures with susceptibility testing. 1, 2
• Consider requesting extended incubation for slow-growing organisms like Streptococcus anginosus group, which commonly causes abscesses and may require 2-4 days for growth. 2

Antibiotic Management

Broaden antibiotic coverage immediately to include Gram-positive, Gram-negative, and anaerobic organisms while awaiting repeat culture results. 1, 3

Empiric Regimen Options:

• Vancomycin PLUS piperacillin-tazobactam (preferred for broad coverage including MRSA and anaerobes). 1
• Alternative: Vancomycin PLUS a carbapenem (ertapenem, meropenem). 1
• Alternative: Vancomycin PLUS ceftriaxone AND metronidazole. 1

Why Your Initial Regimen Failed:

• Cephalexin (Keflex) lacks MRSA coverage and has no anaerobic activity—community-acquired MRSA now accounts for the majority of purulent skin infections. 1
• Clindamycin alone may be inadequate if the organism is clindamycin-resistant (increasingly common) or if Gram-negative or resistant anaerobes are present. 1
• Neither agent provides adequate coverage for the polymicrobial flora (mixed aerobic-anaerobic organisms) commonly found in treatment-refractory abscesses. 1, 3

Critical Pitfalls to Avoid

Do not rely solely on antibiotics without complete surgical drainage—this is the most common error leading to treatment failure. 1, 2, 3

• Antibiotics have limited penetration into abscess cavities, particularly mature abscesses with thick capsules and low pH environments that inactivate many antimicrobials. 4
• Studies demonstrate that drainage alone often suffices for simple abscesses, but your patient has a complicated abscess requiring both complete drainage AND appropriate antibiotics. 1, 3
• Inadequate antibiotic coverage after drainage of complicated abscesses results in significantly higher recurrence rates (28.6% vs 4% in one study). 3

Monitoring and Follow-up

Ensure close follow-up within 48-72 hours to assess clinical response. 1, 2

• If bacteremia is suspected (fever, systemic toxicity), obtain blood cultures before starting new antibiotics and repeat every 24-48 hours until clearance is documented. 2
• Consider repeat imaging (ultrasound or CT) if the patient fails to improve despite complete drainage and broad-spectrum antibiotics, as this may indicate additional undrained foci. 2
• Once culture results return, narrow antibiotics to targeted therapy based on susceptibilities. 1, 2
• Complete a full antibiotic course (typically 7-14 days depending on severity and clinical response) after definitive surgical drainage. 2, 3

Special Considerations

Investigate for underlying conditions if this is a recurrent or unusually refractory abscess. 2

• Streptococcus anginosus group bacteremia has been associated with underlying malignancies, particularly colon cancer. 2
• Consider diabetes, immunosuppression, or other predisposing factors that may impair healing. 1