What's the next step in managing a patient with Methicillin-Susceptible Staphylococcus aureus (MSSA) bacteremia, likely due to thrombophlebitis from an intravenous (IV) infiltrative site, who is currently on cefazolin?

Management of MSSA Bacteremia with Thrombophlebitis

For a patient with MSSA bacteremia due to thrombophlebitis from an IV infiltrative site who is on day 2 of cefazolin with persistent local symptoms, surgical exploration and drainage of the infected site is urgently needed, even though CT is negative for abscess. 1

Source Control

• Surgical drainage of the infiltrative site is critical for optimal therapy, as the Infectious Diseases Society of America strongly emphasizes that "in most cases of abscess, drainage is critical for optimal therapy" 1
• Early source control is a key evidence-based practice in the treatment of S. aureus bacteremia and should be prioritized alongside appropriate antibiotic therapy 1
• Despite negative CT findings, the persistent edema and tenderness suggest a potential collection that requires surgical exploration 1

Antibiotic Management

• Continue cefazolin as it is an appropriate first-line therapy for MSSA bacteremia 1, 2
• Cefazolin is considered equivalent to antistaphylococcal penicillins (oxacillin, nafcillin) for treating MSSA infections 3, 4
• Recent studies show no difference in outcomes between cefazolin and antistaphylococcal penicillins, even with varying oxacillin MICs 5
• The current strain is also susceptible to daptomycin, gentamicin, levofloxacin, oxacillin, and rifampin, but there is no need to change from cefazolin unless clinical failure occurs 3, 1

Monitoring and Follow-up

• Obtain follow-up blood cultures to document clearance of bacteremia 1
• Persistent bacteremia (>48-72 hours) is a poor prognostic sign that should prompt additional investigation for metastatic foci of infection 1
• Consider echocardiography if bacteremia persists beyond 48-72 hours to evaluate for possible endocarditis 3, 1
• If surgical exploration does not reveal a drainable collection, consider MRI of the affected area as it is more sensitive than CT for detecting soft tissue infections 1

Duration of Therapy

• For uncomplicated bacteremia with adequate source control, a 2-3 week course of cefazolin is recommended 1
• Longer therapy (4-6 weeks) may be needed if there are complications such as endocarditis, osteomyelitis, or persistent bacteremia 1, 2
• Monitor for resolution of local and systemic symptoms to guide duration of therapy 1

Potential Pitfalls and Considerations

• Do not add gentamicin to the regimen as it increases nephrotoxicity without improving clinical outcomes 3
• If the patient has brain abscess or CNS involvement, nafcillin would be preferred over cefazolin due to better blood-brain barrier penetration 3, 2
• Monitor for potential adverse effects of cefazolin including seizures (with high doses in renal impairment), false positive glucose tests, and gastrointestinal symptoms 6
• If treatment failure occurs with cefazolin, consider the possibility of the cefazolin inoculum effect and switch to an alternative agent such as nafcillin or ceftaroline 7

Key Takeaways

• Surgical drainage of the infected site is the most urgent next step, despite negative CT findings 1
• Continue cefazolin as appropriate definitive therapy for MSSA bacteremia 1, 8
• Obtain follow-up blood cultures to document clearance of bacteremia 1
• Consider echocardiography if bacteremia persists beyond 48-72 hours 3, 1