Organism-Specific Therapies

Endocarditis due to group B, C, or G streptococci should be treated with the regimen recommended for relatively penicillin-resistant streptococci (Table 80-2).
Killing of enterococci requires the synergistic activity of a cell wall-active agent and an aminoglycoside (gentamicin or streptomycin) to which the isolate does not exhibit high-level resistance. The aminoglycoside can be discontinued in those pts who have responded satisfactorily if toxicity develops after 2-3 weeks of treatment. If there is high-level resistance to both aminoglycosides, the cell wall-active agent should be given alone for 8-12 weeks, or—for Enterococcus faecalis—high-dose ampicillin plus ceftriaxone or cefotaxime can be given. If the isolate is resistant to all commonly used agents, surgical therapy is advised (see below and Table 80-3).
For staphylococcal NVE, the addition of 3-5 days of gentamicin to a β-lactam antibiotic does not improve survival rates and is not recommended.
Although this regimen has not yet been approved by the U.S. Food and Drug Administration, daptomycin (6 mg/kg IV qd; or, as some experts prefer, 8-10 mg/kg IV qd) has been recommended for endocarditis caused by S. aureus isolates with a vancomycin minimal inhibitory concentration (MIC) of ≥2 µg/mL. These isolates should be tested to document daptomycin sensitivity.
Staphylococcal PVE is treated for 6-8 weeks with a multidrug regimen. Rifampin is important because it kills organisms adherent to foreign material. The inclusion of two other agents in addition to rifampin helps prevent the emergence of rifampin resistance in vivo. Testing for gentamicin susceptibility should be performed before rifampin is given; if the strain is resistant, another aminoglycoside, a fluoroquinolone, or another active agent should be substituted.
Empirical therapy (either before culture results are known or when cultures are negative) depends on epidemiologic clues to etiology (e.g., endocarditis in an IV drug user, health care-associated endocarditis).
- - In the setting of no prior antibiotic therapy and negative blood cultures, S. aureus, CoNS, and enterococcal infection are unlikely; empirical therapy in this situation should target nutritionally variant organisms, the HACEK group, and Bartonella.
- - If negative cultures are confounded by prior antibiotic therapy, broader empirical therapy is indicated and should cover pathogens inhibited by the prior therapy.

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