Most Eases of bacterial endocarditis involve infection with viridans streptococci, enterococci, coagulase-positive staphylococci or coagulase-negative staphylococci. The choice of antibiotic therapy for bacterial endocarditis is determined by the identity and antibiotic susceptibility of the infecting organism, the type of cardiac valve involved (native or prosthetic) and characteristics of the patient, such as drug allergies. Antibiotic therapies discussed in this report are based on recommendations of the American Heart Association. Treatment with aqueous penicillin or ceftriaxone is effective for most infections caused by streptococci. A combination of penicillin or ampicillin with gentamicin is appropriate for endocarditis caused by enterococci that are not highly resistant to penicillin, Vancomycin should be substituted for penicillin when high-level resistance is present. Resistance of enterococci to multiple antibiotics including vancomycin is becoming an increasing problem. Native valve infection by methicillin-susceptible staphylococci is treated with nafcillin, oxacillin or cefazolin. The addition of gentamicin for the first three to five days may accelerate clearing of bacteremia. Infection of a prosthetic valve by a staphylococcal organism should be treated with three antibiotics: oral rifampin and gentamicin and either nafcillin, oxacillin, cefazolin or vancomycin, depending on susceptibility to methicillin. Vancomycin is substituted for penicillin in patients with a history of immediate-type hypersensitivity to penicillin.
