Vancomycin is a narrow-spectrum bactericidal antibiotic used primarily for treatment of serious staphylococcal infections. It is the alternative therapy of choice when the penicillins and cephalosporins cannot be used. Vancomycin is also used in (1) methicillin-resistant Staphylococcus aureus infections; (2) streptococcal endocarditis in conjunction with an aminoglycoside in patients intolerant of penicillin or ampicillin; (3) infections, including those involving prosthetic devices, caused by gram-positive organisms with multiple antibiotic resistance; (4) antibiotic-induced enterocolitis caused by Clostridium difficile; and (5) prophylaxis for endocarditis in patients who are at risk and cannot tolerate a penicillin, cephalosporin, or erythromycin. The major toxic effect associated with the use of vancomycin is ototoxicity, which may develop when serum levels exceed 30 micrograms/ml.