What is the empiric antibiotic regimen for a psoas abscess?

Empiric Antibiotic Therapy for Psoas Abscess

For psoas abscess, empiric antibiotic therapy should include vancomycin plus an agent active against enteric gram-negative bacilli, such as piperacillin-tazobactam, ampicillin-sulbactam, or a carbapenem. 1

Microbiology and Rationale

• Psoas abscess can be classified as primary (hematogenous spread) or secondary (direct extension from adjacent structures) 2
• In primary psoas abscess, Staphylococcus aureus is the most common pathogen, with increasing prevalence of MRSA in many communities 1, 2
• Secondary psoas abscesses often have polymicrobial etiology with gram-negative organisms (especially E. coli) and anaerobes predominating, particularly when originating from gastrointestinal or genitourinary sources 2, 3

Recommended Empiric Antibiotic Regimens

Initial Empiric Therapy

• Vancomycin (for MRSA coverage) 1 PLUS one of the following:
• Piperacillin-tazobactam 1
• Ampicillin-sulbactam 1
• Carbapenem (imipenem-cilastatin, meropenem, or ertapenem) 1

Alternative Regimens

• Vancomycin plus ceftriaxone and metronidazole 1
• Vancomycin plus fluoroquinolone and metronidazole 1

Treatment Duration and Approach

• Antibiotics should be administered intravenously initially 1
• Once the patient shows clinical improvement and bacteremia has cleared, transition to oral antibiotics is appropriate 1
• Total duration of antibiotic therapy should be 2-3 weeks 1, 4
• Drainage of purulent material is essential for optimal therapy 1
  • CT-guided percutaneous drainage is appropriate for most cases 5, 6
  • Small abscesses (<2-3 cm) may be treated with antibiotics alone 5
  • Surgical drainage may be necessary for complex or recurrent abscesses 2, 5

Definitive Therapy Based on Culture Results

• For MSSA: Switch to cefazolin or antistaphylococcal penicillin (nafcillin or oxacillin) 1
• For gram-negative organisms: Tailor therapy based on susceptibility results
• Repeat imaging studies should be performed in patients with persistent bacteremia to identify undrained foci of infection 1

Special Considerations

• For immunocompromised patients, broader empiric coverage is essential due to the wider spectrum of potential pathogens 1
• In cases where the psoas abscess is secondary to spinal infection, treatment of the primary source (spondylodiscitis, vertebral osteomyelitis) is crucial 4
• When secondary to Crohn's disease or other gastrointestinal pathology, surgical management of the underlying condition may be necessary for definitive treatment 3, 6

Common Pitfalls to Avoid

• Delay in diagnosis due to nonspecific symptoms; maintain high index of suspicion in patients with fever, flank/back pain, and hip flexion contracture 3, 4
• Inadequate drainage of abscess leading to treatment failure or recurrence 2, 5
• Failure to identify and treat the primary source of infection in secondary psoas abscesses 4
• Premature discontinuation of antibiotics before complete resolution of infection 1, 4