Treatment of Streptococcus mitis Endocarditis

Introduction to Treatment Guidelines

The American Heart Association recommends intravenous penicillin G, ampicillin, or ceftriaxone for 4 weeks, with the addition of gentamicin for the first 2 weeks in cases with penicillin MIC >0.1 μg/mL for the treatment of Streptococcus mitis endocarditis 1, 2

For penicillin-susceptible strains (MIC ≤0.125 mg/L), the European Society of Cardiology recommends a standard 4-week regimen of penicillin G, ampicillin, or ceftriaxone 2, 3
For uncomplicated native valve endocarditis with normal renal function, a 2-week regimen of penicillin G, ampicillin, or ceftriaxone plus gentamicin can be used 2, 3

The American Heart Association recommends extended therapy duration of 6 weeks for prosthetic valve endocarditis, with penicillin, ampicillin, or ceftriaxone plus gentamicin for the first 2 weeks 1, 2, 4

The American Heart Association recommends weekly monitoring of vancomycin and gentamicin blood concentrations and regular renal function tests when using potentially nephrotoxic antibiotics 1
Gentamicin can be given once daily in patients with normal renal function when treating susceptible streptococci 3

The European Society of Cardiology notes that S. mitis is part of the viridans streptococci group and has increasing rates of penicillin resistance (>30% of S. mitis strains show intermediate or full resistance) 2, 5
Bactericidal drug combinations are preferred over monotherapy for tolerant organisms 2, 5
Consultation with an infectious disease specialist should be considered for all patients with infective endocarditis, especially those with resistant organisms 1