Vials and Containers
Vial Coring: When a Needle Cuts the Stopper, and Why You Often Cannot See It
Vial coring is a needle cutting a piece of rubber out of a vial’s stopper. The piece can end up in the solution or inside the needle. This page sets out what the published studies measured, why many fragments are invisible, what raises the risk, how stoppers are tested for it, and what labeling asks for. Research-material handling education only — it recommends no needle and no technique.
The short answer
- Coring is real and measurable. Studies have recorded it in 10.5% of single entries and 17.3% of samples from repeatedly punctured vials.
- Most of it is hard to see. Nearly half the cores in one study and every particle in another were invisible to the eye.
- Puncture count matters. Multiple-use vials are a named risk factor, and the 30 mL ceiling on multiple-dose vials exists to limit stopper punctures.
- The stopper matters as much as the needle. Thickness, hardness and rubber composition all change the rate.
- A visible fragment ends the vial. Published cases discard the contents rather than try to remove it.
Coring and fragmentation
A vial’s stopper is an elastomer — a synthetic rubber — that a needle must pass through. Two different things can go wrong on the way. In coring, the needle shears a core or sliver out of the closure, sometimes a long one. In fragmentation, the needle abrades the rubber and leaves smaller, irregular particles. The distinction comes from West Pharmaceutical Services, a stopper manufacturer, which notes that the two words are often used as if they meant the same thing. For anyone looking at a vial the practical result is the same: rubber where there should only be solution.
A 2025 engineering study from a drug maker’s device team adds the mechanism: the needle deforms the rubber before it cuts it, and elastomers that stretch further before failing and stiffen as they deform shed fewer particles (PMID 40300814).
What the studies measured
Rates vary widely because needles, stoppers and the number of entries vary. A 2023 review letter quotes a range of 3% to 97% across published work (PMC10691600). Two studies with clear counts:
| Study | Set-up | Coring | What else it found |
|---|---|---|---|
| Campagna et al., Eur Radiol 2013 (PMID 22865273) | 200 vials of prednisolone acetate, each entered once with a large-bore cutting bevelled needle | 21 of 200 (10.5%) | 11 of the 21 cores were seen in the syringe; the other 10 were found only after the syringe and needle were taken apart and rinsed. Cores measured 0.6 to 1.1 mm. |
| Chotikawanich et al., Heliyon 2022 (PMID 35592659) | 150 samples from repeatedly punctured 50 mL multiple-dose propofol vials, three needle sizes, two entry angles | 26 of 150 (17.3%) | Coring rose with needle bore; the authors concluded bore size mattered regardless of the angle of entry. |
Why you often cannot see it
The most useful finding for anyone inspecting a vial is how much coring escapes the eye. In the 2013 study, only 11 of the 21 cores were visible in the syringe; the other 10 were found only when the syringe and needle were dismantled and rinsed. In a 2021 study of 800two-millilitre vials of saline, no rubber particle was visible to the naked eye in any sample, but microscopy of the filtered liquid found particles in 10% to 33% of the samples drawn through standard needles. Samples drawn through needles with a built-in 5 µm filter showed none (PMID 36474986).
So a clean-looking vial is not proof of a clean vial. Inspection is still worth doing — it is the only check available at the bench, and it catches the larger cores — but it sets a floor on what you know, not a ceiling.
What raises the risk
The 2025 review by the Research and Safety in Therapeutics Committee of the American Society of Retina Specialists (PMID 40672691) lists four associated factors: larger-bore needles, perpendicular needle entry, multiple-use vials and thicker rubber stoppers, and adds that stopper composition influences the rate. West’s technical note groups the causes the same way, by closure (hardness and thickness of the rubber where it is pierced), needle (sharpness, bevel, size, surface coating) and handling (speed and angle of entry, and whether a needle is reused).
The factor that most concerns a multiple-dose vial is the number of entries. Every puncture is another chance to cut the rubber, and the 2022 study above found coring in vials that had been entered repeatedly. That is the reason the U.S. Pharmacopeia caps multiple-dose vials at a withdrawable total of 30mL: FDA’s 2015 guidance gives the purpose as limiting punctures of the stopper, which reduces the risk of compromising the vial and contaminating its contents. The peptide vial size page covers that ceiling in full.
How stoppers are tested for it
Stoppers for injectable products are tested for fragmentation before they are used. Under the older U.S. Pharmacopeia chapter <381>, fragments were counted by eye, which limited the count to particles larger than about 50 microns. The newer chapter <382> has each stopper pierced four or more times by needle and examined under a microscope, reporting particles larger than 150 microns in any dimension (West Pharmaceutical Services, May 2022).
That change is not settled. A testing laboratory reports that FDA raised concerns about the larger allowable particle size, citing a lack of supporting safety data, and that the fragmentation test was held back from the December 2025 version of <382> while limits are worked out. The standard itself is still moving, which is one more reason not to treat a stopper as something that cannot shed material.
What labeling asks for
Approved injectables carry a standard instruction that covers it. The bacteriostatic water for injection label reads: “Parenteral drug products should be inspected visually for particulate matter and discoloration prior to administration, whenever solution and container permit.” Its precautions add a check of reconstituted drugs for clarity and freedom from unexpected precipitation or discoloration.
Where a fragment is seen, the published case reports agree on the outcome: the contents are discarded and a new vial is used. In the case described in the 2023 letter, a dark particle was noticed in a vial before use, and both the drawn liquid and the vial were discarded. Nobody in these reports tries to retrieve the fragment. For research material, a vial with visible rubber in it is a vial whose contents can no longer be described as clean — and, as the section above shows, a vial without visible rubber is not guaranteed to be free of it.
Common mistakes about coring
- “The solution looks clear, so there is no rubber in it.” In two studies most or all particles were invisible to the eye.
- “Coring only happens with old vials.” It was recorded on a single entry into a vial.
- “A fragment can be fished out.” Published cases discard the contents; a cut stopper has already shed material.
- “The stopper reseals, so puncture count does not matter.” Repeated entry is a named risk factor, and it is why multiple-dose vials have a size ceiling.
- “Coring is a needle problem only.” Stopper thickness, hardness and composition matter as much as the needle.
What Medibact supplies
Medibact stocks USP-grade bacteriostatic water produced in an FDA-registered U.S. facility, in the 30 mL multiple-dose format, sold for research use only. Medibact does not sell needles, peptides or any product named in the studies on this page and is not affiliated with West Pharmaceutical Services, Hospira or any organisation named here; their documents are cited because they describe stoppers and inspection, and nothing here describes how any product should be used.
Where this sits in the rest of the reference
FAQ
What is vial coring?
Vial coring is when a needle passing through a vial’s rubber stopper cuts a piece out of it. The piece can fall into the solution or lodge inside the needle and be drawn out with the liquid. The term comes from the needle acting like a corer, punching a plug out of the rubber.
Is coring the same as fragmentation?
Not quite, although the words are often used interchangeably. A stopper manufacturer, West Pharmaceutical Services, describes coring as a needle shearing a core or sliver out of the closure, and fragmentation as smaller, irregular particles abraded from the rubber as the needle passes through. Both put stopper material where it does not belong.
How common is vial coring?
It depends heavily on the needle, the stopper and how many times the vial is entered. In a 2013 study of 200 single entries, 10.5% produced a core; in a 2022 study of repeatedly punctured multiple-dose vials, 17.3% did. A 2023 review letter quotes a range from 3% to 97% across the literature.
Can you always see a cored fragment?
No. In the 2013 study, 10 of 21 cores were invisible until the equipment was taken apart. In a 2021 study of 800 small vials, no rubber particle was visible to the naked eye in any of them, yet microscopy found particles in 10% to 33% of the samples drawn through standard needles. Visual inspection catches some coring, not all of it.
What makes coring more likely?
A 2025 review by the American Society of Retina Specialists lists larger-bore needles, perpendicular entry, multiple-use vials and thicker rubber stoppers, and notes that stopper composition matters too. A stopper manufacturer adds rubber hardness, needle sharpness and design, and reusing a needle. Repeated punctures of the same stopper are the common thread in multiple-dose vials.
What happens to a vial in which a fragment is seen?
In the published case reports, the contents were discarded and a new vial used; nobody tried to remove the fragment. Product labeling for bacteriostatic water asks for a visual check for particulate matter and discoloration whenever the solution and container permit. For research material the same logic holds: a visible particle means the vial’s contents can no longer be described as clean.
Why do multiple-dose vials matter for coring?
Because every entry is another chance to cut the stopper. USP caps a multiple-dose vial at a withdrawable total of 30 mL, and FDA’s 2015 guidance gives the reason as limiting punctures of the stopper, which reduces the risk of compromising the vial and contaminating its contents.
Is this medical advice?
No. This page is research-material handling education drawn from published studies, a stopper manufacturer’s technical notes and product labeling. It does not recommend any needle, technique, dose or route. Medibact is not affiliated with West Pharmaceutical Services, Hospira or any organisation named here.
Educational use only — not medical advice. This guide summarizes information reported in published research and community practice for educational purposes. It is not medical advice and not a recommendation to use any compound. Any doses, schedules, or combinations shown are examples of what has been reported, not instructions for you. Many peptides described here are research compounds that are not FDA-approved for the uses discussed and may be investigational or restricted. Effects, risks, and legal status vary; individual needs and results vary. Consult a qualified, licensed healthcare professional before making any decision. Do not use this content to diagnose, treat, or dose yourself.