[Antibiotic therapy of infectious endocarditis (when, with what drug, how long?]

The aim of antibiotic therapy in bacterial endocarditis is to sterilize infected cardiac structures and vegetations. Pathogenic organisms are present in great numbers within vegetations and abscess-formations. They exist in a state of reduced metabolic activity so that they are able to tolerate even therapeutic levels of bactericidal antibiotic concentrations. Because vegetations are normally devoid of blood vessels, impregnation with antibiotic agents is poor. Effective therapy is greatly improved by identification of the pathogenic organism involved. With very few exceptions isolation is possible prior to initiation of antibiotic therapy. In acute cases with signs of septicemia, however, therapy cannot await results of bacterial testing. In these patients selection of antibiotic agents is based on associated evidence such as the presence of a prosthetic heart valve or intravenous drug addiction. Once the pathogen has been identified antibacterial therapy should be tailored according to the test results. Bactericidal antibiotics should always be preferred over bacteriostatic agents; in many cases adequate bactericidal levels can only be achieved by combining various agents, such as ampicillin and gentamycin for treatment of enterococcal endocarditis. Dosing intervals must take into account the resulting trough levels, which should always exceed the minimal inhibitory concentrations for a specific bacterial strain. In cases with inadequate control of infection, congestive heart failure resulting from valve dysfunction, and abscess formation, surgery as the only means of eradicating the infection and restoring cardiac performance should not be delayed.