Only bactericidal therapy is effective in treating endocarditis. Antimicrobial therapy should be dosed to optimize sustained bactericidal serum concentrations throughout as much of the dosing interval as possible. In vitro determination of the minimum inhibitory concentration should be performed routinely.
Therapy for infective endocarditis (IE) should be targeted to the organism isolated from blood cultures; cultures are positive in over 90 percent of patients with IE. For patients with suspected IE who present without acute symptoms, empiric therapy is not always necessary, and therapy can await blood culture results.
For acutely ill patients with signs and symptoms strongly suggestive of IE, empiric therapy may be necessary. Such empiric therapy should be administered ONLY after at least two (preferably three) sets of blood cultures have been obtained from separate venipunctures．
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In general, empiric therapy should cover staphylococci (methicillin susceptible and resistant), streptococci, and enterococci. Vancomycin (15 to 20 mg/kg/dose every 8 to 12 hours, not to exceed 2 g per dose) is an appropriate choice for initial therapy in most patients.
The optimal antibiotic regimen depends upon the causative organism and in vitro susceptibility results. The treatment of native valve endocarditis caused by viridans streptococci, other streptococci, enterococci, staphylococci, HACEK organisms, other gram-negative organisms, and culture-negative endocarditis is discussed in the sections devoted to these organisms.
The duration of therapy in patients with native valve endocarditis ranges up to six weeks and depends on the pathogen and site of valvular infection. Most patients are treated parenterally with regimens given for either four or six weeks. In general, longer (six-week) treatment regimens are used in patients with highly virulent or more resistant pathogens, those with secondary cardiac or extracardiac complications, and in patients with infections of long duration prior to diagnosis.
Early consultation with a cardiac surgeon should be obtained for all cases in which complications are observed or expected (such as in infections involving prosthetic valves or in the presence of moderate to severe heart failure or heart block or systemic emboli). In addition, consultation by specialists in infectious diseases and/or cardiology may be useful. Patients with endocarditis require careful regular clinical follow-up that includes serial physical examinations and obtaining follow-up blood cultures to document clearance of bacteremia.