Issues related to the antimicrobial therapy of native valve infective endocarditis (IE) will be reviewed here. The pathogenesis of vegetation formation, complications, and indications for surgery are discussed separately. (See "Pathogenesis of vegetation formation in infective endocarditis" and "Complications and outcome of infective endocarditis" and "Surgery for native valve endocarditis".)
Bactericidal agents are necessary for effective treatment of endocarditis. Therefore, 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 (MIC) should be performed routinely.
Empiric therapy — In general, 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. Results of blood cultures are usually available within one to three days, and an accurate diagnosis is a critical first step in designing a management strategy. (See "Clinical manifestations and diagnosis of infective endocarditis".)
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 and ideally spaced over 30 to 60 minutes.
The choice of empiric therapy should take into consideration the most likely pathogens. 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.