Treatment of Gram-Negative Bacilli Skin Lesions
For gram-negative bacilli skin lesions, initiate broad-spectrum antibiotics with antipseudomonal activity—specifically piperacillin-tazobactam, a carbapenem (such as meropenem), or an antipseudomonal cephalosporin (such as cefepime)—combined with prompt incision and drainage for any abscess or collection. 1
Primary Treatment Strategy
Source Control is Paramount
- Incision and drainage must be performed for all cutaneous abscesses, as antibiotics alone are insufficient without adequate source control 1
- Drainage should be performed promptly, with repeat imaging if bacteremia persists to identify undrained foci 1
- Surgical intervention may be necessary to drain soft-tissue abscesses or for progressive polymicrobial fasciitis 2
Empiric Antibiotic Selection
Initial therapy requires dual-agent coverage for suspected multidrug-resistant gram-negative pathogens:
Start with two antimicrobial agents of different classes with gram-negative activity as initial therapy 2
Recommended first-line regimens include:
The rationale for broad coverage is that Pseudomonas aeruginosa and other gram-negative bacilli are associated with the highest infection-associated mortality 1, 4
De-escalation Strategy
- Once culture and susceptibility results are available, de-escalate to a single appropriate antibiotic 2
- This typically occurs within 48-72 hours of culture collection 2
- Continue single-agent therapy for the remainder of the treatment course, usually 7-14 days 2, 1
Special Clinical Scenarios
Immunocompromised Patients
- Require immediate broad-spectrum coverage due to high mortality risk from gram-negative infections 1
- Should receive vancomycin plus an antipseudomonal agent empirically 1
- Neutropenic patients are at particular risk for gram-negative infections including E. coli, Klebsiella species, and P. aeruginosa 2
- Ecthyma gangrenosum (painful necrotic lesions) is a hallmark of Pseudomonas bacteremia in neutropenic patients and requires urgent treatment 2
Perianal or Perirectal Lesions
- Require coverage for gram-negative, gram-positive, and anaerobic bacteria 1
- Treat with piperacillin-tazobactam or carbapenem 1
Multidrug-Resistant Organisms
- For extended-spectrum β-lactamase (ESBL)-producing organisms, carbapenems are superior to cephalosporins or piperacillin-tazobactam, even when organisms appear susceptible in vitro 2
- Organisms with carbapenemases may require polymyxin (colistin) or aminoglycosides, though evidence is limited 2
Treatment Duration and Monitoring
- Standard duration is 7-14 days for most bacterial skin and soft tissue infections 1, 2
- May be shortened to 24-48 hours if only mild systemic signs are present and adequate drainage is achieved 1
- Switch to oral therapy once clinically improved, afebrile for 48-72 hours, and bacteremia cleared 1
Critical Pitfalls to Avoid
Never Rely on Antibiotics Alone
- Source control through drainage is paramount—antibiotics without drainage will fail 1
Don't Delay Gram-Negative Coverage in High-Risk Patients
- Mortality is highest with gram-negative bacteremia, particularly P. aeruginosa 1, 4
- Inappropriate initial antimicrobial therapy significantly increases mortality, especially in patients with high-risk sources of bacteremia (lung, peritoneum, or unknown source) 4
- In one study, inadequate initial therapy resulted in 38.4% mortality versus 27.4% with appropriate therapy 4
Avoid Monotherapy for Suspected MDR Organisms
- Initial dual therapy is essential until susceptibilities return 2
- Single-agent therapy with cephalosporins has been associated with treatment failure in Enterobacter bacteremia 2
Cefepime Dosing Considerations
- For organisms with cefepime MIC ≥8 mcg/mL, mortality rates exceed 50%, compared to 24% for MIC <8 mcg/mL 5
- Standard dosing of 1-2 grams every 12 hours may be inadequate for serious infections with higher MICs 5