Staphylococcal endocarditis. Laboratory and clinical basis for antibiotic therapy.

Antibiotic therapy for staphylococcal endocarditis is based on in vitro susceptibility, antibiotic efficacy in experimental endocarditis, and clinical experience. Native valve endocarditis due to Staphylococcus aureus in non-addicts is treated with four to six weeks of a penicillinase-resistant penicillin, a cephalosporin, or vancomycin. An aminoglycoside can be added for the initial three to five days, but longer-term multiple-drug therapy (adding an aminoglycoside and rifampin) is reserved for unresponsive infection. Right-sided native valve endocarditis in addicts usually responds to less vigorous therapy than that for native valve endocarditis in non-addicts. Vancomycin is the drug of choice for endocarditis due to methicillin-resistant S. aureus. Intrinsic methicillin-resistance in Staphylococcus epidermidis is often cryptic, requiring special tests for detection. Methicillin-resistant S. epidermidis is the major cause of prosthetic valve endocarditis. Vancomycin, rifampin, and gentamicin therapy for two weeks, followed by vancomycin plus rifampin, is recommended for treating this infection. Despite potent antimicrobial therapy, surgery is important in the therapy of complicated endocarditis, particularly prosthetic valve endocarditis.