Inclusion Criteria:

1. Written informed consent has been obtained;
2. Male or female ≥18 years of age;
3. IVDU (as confirmed by history of drug abuse within the past 3 months or recent needle track marks);
4. Definite or possible IE according to the modified Duke Criteria (see Appendix A); [17 ];
5. Two blood cultures positive for S. aureus obtained within 96 hours prior to first dose of study medication acquired by fresh venipuncture using aseptic technique and analyzed at the local laboratory (see Appendix B).

Exclusion Criteria:

1. Intravascular foreign material in place at the time that the positive blood culture was drawn (e.g., intracardiac pacemaker wires, percutaneous or implanted venous catheters, vascular grafts), (exception: vascular stents that have been in place for >6 months or permanent pacemaker wires attached via epicardial leads are allowed);

2. High likelihood of LIE as indicated by:

   1. Prior diagnosis of predisposing left-sided valvular pathology (e.g., rheumatic heart disease, bicuspid aortic valve); or
   2. Findings on screening examination of left-sided valvular pathology (e.g., diastolic murmur of aortic insufficiency); or
   3. Findings on screening examination of major systemic emboli to visceral organs (e.g. cerebral or splenic infarct). Patients may be included if their only findings are consistent with microvascular phenomena due to immune complexes (e.g., splinter hemorrhages, conjunctival petechiae, Roth's spots, Osler's nodes, Janeway's lesions, microhematuria).

   Note: Any patient enrolled in the study that is subsequently found to have LIE may be continued in the trial if determined to be clinically improving by the Investigator.

3. Prosthetic heart valve;
4. Baseline Creatinine clearance of <30 mL/min (as calculated by the Cockcroft-Gault equation using actual body weight);
5. Baseline CPK value 5 X upper limit of normal (ULN) in conjunction with symptoms of myalgia or baseline CPK value 10 X ULN without symptoms;
6. Alanine aminotransferase (ALT) >5 X ULN;
7. Aspartate aminotransferase (AST) >5 X ULN;
8. Moribund clinical condition (i.e. high likelihood of death within 3 days after randomization);
9. Shock or hypotension (supine systolic blood pressure <80 mm Hg) or oliguria (urine output <20 mL/h) unresponsive to fluids or pressors within 4 hours;
10. Known pneumonia or osteomyelitis;
11. Polymicrobial infection or bacteremia due to a pathogen other than S. aureus;
12. Neutropenia (absolute neutrophil count < 0.5 X 103/μL) and/or lymphopenia (CD4 lymphocytes <0.2X 103/μL);
13. Anticipated to require non-study antibiotics that may be potentially effective against S. aureus;
14. Prior gentamicin therapy > 1 day;
15. Documented history of significant allergy or intolerance to any of the study medications;
16. Unlikely to comply with study procedures;
17. Pregnant or nursing. All females with childbearing potential will have a pregnancy test performed at the local laboratory.
18. Female of childbearing potential and not willing to practice barrier methods of birth control (e.g., condoms or diaphragms together with spermicidal foam or gel) during treatment and for at least 28 days after treatment with study medication