What it is
Vancomycin is an antibiotic whose core is a short peptide: seven amino acids, folded and cross-linked into three rings, with two sugars attached. The US injection label calls it "a tricyclic glycopeptide antibacterial derived from Amycolatopsis orientalis (formerly Nocardia orientalis)" — a soil bacterium that makes it by fermentation. Vancomycin hydrochloride is C66H75Cl2N9O24·HCl, molecular weight 1,485.71.
It is a peptide in the chemist's sense, not the supplement-market sense. The seven building blocks include unusual, chlorine-carrying amino acids, and the rings are formed by bonds between side chains, which is why the label's chemical name reads like a ring system rather than a sequence of amino acids.
How it works
The label's mechanism is short: vancomycin's bactericidal action "results primarily from inhibition of cell-wall biosynthesis," and it "alters bacterial-cell-membrane permeability and RNA synthesis." The wall in question is peptidoglycan, the sugar-and-peptide mesh that holds a bacterium's shape; human cells have none.
The same label states its limits: vancomycin is not active against Gram-negative bacilli, mycobacteria or fungi. Its labelled uses centre on Gram-positive bacteria, above all staphylococci, including methicillin-resistant strains.
Two routes, two different drugs in practice
| Route | What the label says it treats | Why |
|---|---|---|
| Intravenous | Septicaemia, infective endocarditis, skin, bone and lower respiratory tract infections caused by susceptible bacteria, in adults and children including newborns | Infused vancomycin reaches the blood and tissues |
| Oral (Vancocin capsules) | C. difficile-associated diarrhoea; staphylococcal enterocolitis | Swallowed vancomycin is barely absorbed and stays in the gut |
The oral label spells out the boundary in both directions: intravenous vancomycin "is not effective" for these gut infections, and oral vancomycin "is not effective for other types of infections."
What the labels' trials show
The oral label reports two trials of Vancocin 125 mg four times daily for 10 days in 266 adults with C. difficile diarrhoea. Clinical success — diarrhoea resolved and no severe abdominal discomfort on day 10 — was 81.3% (of 134) in one trial and 80.8% (of 125) in the other; median time to resolution was 5 and 4 days. These figures are for the vancomycin arm; the label presents them without a placebo comparison.
The older injection labels carry no modern trial table. They rest on decades of use, and the newer generic labels list indications by infection site rather than by trial.
Doses on the label
Reported from the labels, for reference; the dose for any patient is set by the treating team.
| Use | Adults (label) |
|---|---|
| Systemic infections (IV) | 2 g a day, divided as 500 mg every 6 hours or 1 g every 12 hours, each infused over at least 60 minutes; adjusted for kidney function |
| C. difficile diarrhoea (oral) | 125 mg four times daily for 10 days |
The injection label gives a mean elimination half-life of 4 to 6 hours with normal kidney function and 7.5 days in people without kidney function, which is why blood-level monitoring and kidney-based dosing run through the whole label.
Safety
The injection label's warnings are, in order: infusion reactions (including the itching and flushing of the face, neck and upper body it calls the "vancomycin infusion reaction", plus low blood pressure and, rarely, cardiac arrest with rapid infusion), kidney injury, mainly interstitial nephritis, ototoxicity — tinnitus, hearing loss, dizziness or vertigo, "transient or permanent", with higher risk in older patients and alongside other ear-toxic drugs such as aminoglycosides — severe skin reactions (TEN, SJS, DRESS, AGEP), C. difficile diarrhoea, a rare haemorrhagic occlusive retinal vasculitis, and low white-cell counts.
In pregnancy, the label cites small published studies, including one with no hearing loss or kidney toxicity at 3 months in infants exposed in the second or third trimester; it does not describe the data as establishing safety.
Where it stands
- Approved in the US for decades. Drugs@FDA's electronic record lists 43 vancomycin applications, the oldest dated 1983 (ANDA 061667) and 1986 (Vancocin, NDA 050606, now held by ANI Pharmaceuticals); earlier history is not in that database (openFDA, 2026-10-11).
- Generic and widely available as injection and intravenous products and as oral capsules or solution.
- Research record: PubMed indexes 44,407 records, 755 tagged as randomised trials (2026-10-11).
Related reading
Dalbavancin is a newer member of the same glycopeptide family, carrying a fatty tail that keeps it in the body for weeks. The structure vancomycin attacks is explained in the library's account of the bacterial cell wall, and another peptide-based hospital anti-infective, the antifungal micafungin, works on the fungal cell wall instead. Outside hospitals, the best-known peptide antibiotic is bacitracin, the ring-shaped peptide in first-aid ointments.