Empiric Therapy Regimens
Generally, empiric therapy is not instituted in suspected cases of subacute endocarditis until the etiology is identified by blood cultures. If blood cultures are negative but endocarditis is still considered likely, therapy is chosen based on the most likely etiology. Acute endocarditis is usually due to Staphylococcus aureus infection (both methicillin-susceptible and methicillin-resistant), streptococci, and enterococci. Ensure that the blood cultures are obtained prior to initiation of antibiotics. Empiric therapy for such infections would generally depend on whether the endocarditis is of a native or prosthetic valve. [1, 2]
Native valve endocarditis
Gram-positive cocci in clusters:
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Vancomycin 15-20 mg/kg IV q8-12h daily to maintain vancomycin trough or level of 15-20 µg/mL
Gram-positive cocci in pairs or chains:
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Vancomycin 15-20 mg/kg IV q8-12h doses
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Ampicillin or vancomycin and an aminoglycoside (gentamicin or streptomycin) for enterococci
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If vancomycin-resistant Enterococcus infection is suspected, use daptomycin 6 mg/kg IV q24h. [3, 4, 5] Anecdotal reports describe linezolid 600 mg IVPB q12h.
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For intravenous drug users, especially those with right-sided S aureus endocarditis, 2 weeks of therapy with nafcillin plus aminoglycoside is effective
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Penicillin with gentamicin for Gemella species, Abiotrophia defectiva, or Granulicatella species
Gram-negative bacilli:
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First-line treatment: Cefepime 2 g IV q8h for normal renal function
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Second-line treatment (if patient is penicillin or cephalosporin intolerant): Aztreonam 2 g IV q8h for normal renal function
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Antipseudomonal penicillin plus aminoglycoside recommended if Pseudomonas aeruginosa endocarditis is suspected [1]
Additional recommendations for prosthetic valve endocarditis
See the list below:
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For prosthetic valve endocarditis, rifampin 900 mg IV q24h in 3 divided doses is added for treatment of S aureus or coagulase-negative Staphylococcus endocarditis
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Gentamicin 1 mg/kg IV based on ideal body weight; not extended-interval dosing; usually added for treatment of gram-positive endocarditis; synergistic dosing targeting a peak of 3-4 mcg/mL
