Vancomycin (van" koe mye' sin) is a glycopeptide antibiotic produced by Streptococcus orientalis with primary activity against gram positive bacteria. Vancomycin has a large, complex and unusual structure and is believed to act by inhibition of bacterial cell wall synthesis via binding to the cell wall precursor molecules. Vancomycin is active against, and its major use is in therapy of, infections due to methicillin-resistant Staphylococcus aureus (MRSA), including antibiotic-induced pseudomembranous colitis, staphylococcal enterocolitis, bacterial endocarditis, and sepsis. Vancomycin is not well absorbed orally and for systemic infections it is given intravenously. It is frequently used in combination with other antibiotics and started before bacterial sensitivity results are available. For localized or nonsystemic infections, other routes of administration are used, including oral, rectal, topical, inhalational, intrathecal, intraperitoneal, and intraventricular. The recommended parenteral dosage in adults is 500 mg iv every 6 hours or 1000 mg every 12 hours, with modification to achieve a therapeutic range as needed. The recommended oral dosage in the treatment of antibiotic induced pseudomembranous enterocolitis is 125 to 500 mg every 6 hours for 7 to 10 days. Vancomycin is available generically and under several commercial names including Vancoled, Vancor, Lyphocin, and Vancocin in 125 and 250 mg pulvules and as power for injection or oral administration. Vancomycin was first approved for use in the United States in 1958 and it continues to be widely used, particularly with the recent rise in incidence of serious MRSA infections. Vancomycin is largely well tolerated; common side effects include diarrhea, nausea, nephrotoxicity and neutropenia. Uncommon but potentially severe adverse reactions include infusion reactions, flushing reactions, anaphylaxis, nephrotoxicity, ototoxicity, hypersensitivity reactions including Stevens-Johnson syndrome, and drug reactions with rash, eosinophilia and systemic symptoms (DRESS syndrome).