Vancomycin

Vancomycin is a glycopeptide antibiotic that blocks bacterial cell-wall construction. It binds the terminal D-alanyl-D-alanine sequence of cell-wall precursors, disrupting peptidoglycan assembly and causing susceptible bacteria to die.⁵ The drug acts mainly against Gram-positive organisms because its large molecular structure does not readily cross the outer membrane of Gram-negative bacteria.

Intravenous vancomycin is used for serious infections caused by organisms such as Staphylococcus aureus, including methicillin-resistant MRSA, and susceptible streptococci or enterococci. Typical conditions include bloodstream infection, endocarditis, osteomyelitis, pneumonia, and meningitis when the causative organism is susceptible. Oral vancomycin has a different role: it treats intestinal Clostridioides difficile infection, but is not appropriate for systemic infections because little drug enters the bloodstream after oral dosing.¹

Intravenous vancomycin requires individualized dosing and laboratory monitoring because exposure varies substantially among patients. Dosing is adjusted for kidney function, body size, age, and the severity and location of infection; prolonged therapy generally requires measurement of drug exposure, often using the area under the concentration–time curve rather than relying only on a single trough concentration.³

The principal serious toxicity is kidney injury, with risk influenced by high exposure, prolonged treatment, and concurrent nephrotoxic medicines. Infusion too rapidly can produce vancomycin infusion reaction, formerly called “red man syndrome,” characterized by flushing, itching, and sometimes low blood pressure; slowing the infusion and providing appropriate treatment usually controls it.² Less common effects include hearing toxicity, low blood-cell counts, phlebitis, and severe allergic reactions. Oral treatment is usually less nephrotoxic, although systemic absorption can increase in severe colitis or impaired intestinal integrity.

Vancomycin resistance is most clinically significant in enterococci and in some strains of Staphylococcus aureus. Vancomycin-resistant enterococci, or VRE, commonly acquire genes such as vanA or vanB that alter the drug-binding target from D-alanyl-D-alanine to a form with much lower affinity, allowing cell-wall synthesis to continue.⁴

Reduced susceptibility in MRSA can also arise through thicker or altered cell walls, producing strains classified as vancomycin-intermediate or, rarely, vancomycin-resistant. These organisms make susceptibility testing and infectious-disease consultation important when a patient fails to improve. Stewardship limits unnecessary exposure, selects treatment according to cultures and susceptibility results, and avoids using intravenous vancomycin when a narrower or more effective agent is available. Infection-control measures, including hand hygiene and environmental cleaning, help contain VRE and other resistant organisms.

Vancomycin’s route of administration determines whether it acts locally or throughout the body. The drug was isolated in the 1950s from a soil microorganism collected in Borneo, and its early crude preparations were unusually impure, giving rise to the nickname “Mississippi mud”; manufacturing improvements later made it safer and more practical.⁵

Its pharmacology creates several clinical edge cases. Inflammation can increase penetration into the meninges, but cerebrospinal-fluid concentrations are variable, so dosing and combination therapy for bacterial meningitis require specialist guidance. Oral vancomycin can be highly effective for C. difficile because it reaches high intestinal concentrations, yet it does not eradicate colonization reliably and can contribute to selection of resistant organisms. The related drug fidaxomicin is another treatment option for some C. difficile infections, while alternative intravenous agents may be needed for resistant enterococci or vancomycin treatment failure.³

Glycopeptide

A class of antibiotics whose bulky sugar-containing structures inhibit bacterial cell-wall synthesis.

MRSA

Methicillin-resistant Staphylococcus aureus, a staphylococcal strain resistant to many beta-lactam antibiotics.

VRE

Vancomycin-resistant enterococci, enterococcal bacteria able to grow despite clinically relevant vancomycin exposure.

AUC

Area under the concentration–time curve, a measure of total drug exposure used to guide some vancomycin dosing.