Baddour et al Infective Endocarditis in Adults 1451 IE Caused by Staphylococci in the Absence of Prosthetic Valves or Other Prosthetic Material Right-Sided IE in IDUs The addition of gentamicin to nafcillin or oxacillin has tradi- tionally been a standard approach for the treatment of right- sided IE. For example, in IDUs with uncomplicated right-sided S aureus IE (no evidence of renal failure, extrapulmonary metastatic infections, aortic or mitral valve involvement, meningitis, or infection by MRSA), combined short-course (2 weeks) -lactam plus aminoglycoside therapy was highly effective in several studies.91,92,148 In 1 study, 92 patients pro- vided such combination therapy had excellent outcomes, even HIV-infected patients and those who had large tricuspid valve vegetations (>10 mm in diameter). In contrast, short-course regimens with glycopeptides (teicoplanin or vancomycin) plus gentamicin appeared to be less effective for right-sided S aureus IE caused by either MSSA or MRSA strains.148 These glycopeptides may be less effective because of limited bacte- ricidal activity, poor penetration into vegetations, or increased drug clearance among IDUs. A growing body of evidence suggests that the addition of adjunctive aminoglycoside therapy not only is unnecessary for patients with uncomplicated right-sided native valve S aureus IE but may cause harm. 