What it is
A glass cartridge is a small glass tube that holds a liquid medicine inside an injection device. The back end is closed by a rubber plunger. The front end is closed by a thin aluminium cap holding a rubber seal, which the needle passes through. Cartridges sit inside reusable insulin pens, inside many disposable pens, and inside the metal syringes dentists use for local anaesthetic. Pen cartridges commonly hold up to 3 mL; dental ones hold about 1 to 2 mL.
The international standard for pen-cartridge glass calls for the most chemically resistant pharmacopoeial grade, and the inside is commonly coated with a thin film of silicone so the plunger can slide. A cartridge is packaging. Regulators approve the medicine in it, and they judge the cartridge only as part of that finished product.
FDA’s 1999 container closure guidance lists disposable cartridges among the packaging formats for small-volume parenterals and states that cartridges, syringes, vials and ampules are usually made of Type I or II glass, or polypropylene, with stoppers and septa of elastomeric materials. The 2023 text of USP general chapter 660 classifies suitability by hydrolytic-resistance performance: containers meeting Type I performance, such as borosilicate, are suitable for most parenteral products, while Type III soda-lime silica glass usually is not used for them unless stability data show it is satisfactory. ISO 13926-1:2018 required pen-injector cylinders to be made of glass corresponding to pharmacopoeial Type 1.
Component standards include ISO 13926-1:2026 for glass cylinders of cartridge-type needle-based injection systems, ISO 13926-2 and -3 for plunger stoppers and seals, ISO 11608-3 for containers used with needle-based injection systems, and ISO 11499:2014 for dental cartridges of 1.0, 1.7, 1.8 and 2.2 mL. The barrel is commonly siliconised as a lubricant. In cartridges with silicone baked onto the glass, Funke et al. (2016) found that baked-on levels below 100 µg limited silicone migration without compromising device function, with particle counts very low compared with those reported for spray-on siliconised containers.
Who made it and when
The prefilled glass cartridge began in dentistry. Harvey S. Cook, a doctor from Indiana, is credited by the Smithsonian with devising a system of medicine sealed in a glass cartridge while serving with US forces in Europe during the First World War. A Chicago firm, Cook Laboratories, introduced the name “Carpule” in 1922.
Insulin followed about six decades later. In 1985 Novo (now Novo Nordisk) launched the NovoPen, a reusable pen-shaped injector that held a replaceable 1.5 mL insulin cartridge. Later reusable pens took 3 mL cartridges, and disposable pens arrived with the cartridge sealed inside. The pen format has since spread to other injected medicines, including non-insulin diabetes drugs.
The Smithsonian’s National Museum of American History credits Harvey Samuel Cook, a physician in Valparaiso, Indiana, with devising the Carpule system of anaesthetic in a glass cartridge while serving with US forces in Europe in the First World War; he later assigned several patents to Cook Laboratories of Chicago, which introduced the Carpule name in 1922 and filed for a trademark. FDA regulations still define the dental cartridge syringe (21 CFR 872.6770) as a metal syringe body into which a disposable, previously filled glass carpule is placed.
For insulin, the NovoPen (1985) combined a durable dosing mechanism with a disposable, replaceable 1.5 mL cartridge; an early randomised crossover study (Berger et al., 1985, 16 adults with type 1 diabetes, as summarised by Masierek et al.) found no significant differences in blood glucose, HbA1c or hypoglycaemia versus vial and syringe. Reusable pens later moved to 3 mL cartridges, while prefilled disposable pens enclose the cartridge permanently (Masierek et al., 2022). Current FDA labels reflect both formats: Humalog, for example, is supplied as 3 mL single-patient-use cartridges for compatible reusable pens and as prefilled pens.
What the data say
The best-documented danger is sharing. After an injection, blood and skin cells can be drawn back into the cartridge. A study of 120 pen users found biological material in 58% of the cartridges examined. That is why a pen or cartridge can pass infection to the next person even when the needle is changed. US hospitals have had to contact thousands of patients for hepatitis and HIV testing after pens were used on more than one person, although one large military-hospital investigation found no clear evidence that infections had spread.
The container can also fail. Regulators and researchers describe cracking and breakage, glass flakes shed from the inner surface, silicone droplets from the lubricant, and chemicals leaching from rubber or glass into the medicine. No published study was found on the sterility of cartridges refilled outside a manufacturer’s controlled filling process.
Contamination: Le Floch et al. (1998) examined material from needles and cartridges after a single nurse-administered pen injection in 120 patients; non-inert material, including squamous and epithelial cells, was found in 62% of patients, and biological material in 30% of needles and 58% of cartridges. Sonoki et al. (2001) reported regurgitation of blood into insulin cartridges, the mechanism CDC cites in its 2012 reminder that pen use for more than one person is a “never event”. In a Texas military-hospital investigation (Hakre et al., 2012), 1,501 of 2,113 patients prescribed pen injections were tested and no clear evidence of transmission was found.
Container quality: FDA scientists list breakage, flakes and particles among glass-container problems behind reports and recalls (Srinivasan et al., 2019). FDA’s March 2011 advisory on glass lamellae concerned small-volume vials, flagging high-pH, citrate- or tartrate-buffered and room-temperature products as higher risk. Silicone droplets migrate from baked-on layers under agitation, scaling with silicone load (13 versus 94 µg per cartridge) and headspace (Funke et al., 2016). FDA’s 2026 draft guidance names delamination, particulates and leachables as incompatibility risks. The Xylocaine Dental label attributes most cracking of glass cartridges to extruded plungers.
Regulatory picture
The FDA does not approve empty cartridges. It approves a medicine together with its container, and the drug maker must show that the glass, rubber and cap protect the medicine without contaminating it. Major changes to that container need FDA approval before products made with the change are distributed. A cartridge that is sold empty, or emptied and refilled with something else, carries none of that approval. The devices that hold cartridges are separate: pen injectors and dental cartridge syringes are regulated as medical devices.
On sharing, the FDA (since 2009) and the CDC (since at least 2012) have said that insulin pens and cartridges are for one person only, even when the needle is changed. Since 2015 the FDA has required “For single patient use only” warnings on multi-dose diabetes pens. In August 2026 the FDA proposed a replacement for its 1999 guidance on drug containers.
Under 21 CFR 211.94, containers and closures must not be reactive, additive or absorptive so as to alter the drug, must protect against foreseeable contamination, and must be clean and, where indicated, sterilised and depyrogenated; 21 CFR 211.113(b) requires validated aseptic and sterilisation processes for sterile products. Container closure information is part of the NDA, ANDA or BLA; for NDAs, 21 CFR 314.70(b)(2)(vi) treats changes to a container closure system that controls the drug delivered, or to the type or composition of a packaging component that may affect impurities, as major changes needing prior approval.
FDA’s draft guidance of 2026-08-14 (docket FDA-2026-D-7957) would supersede the 1999 guidance, extends to containers that are device constituents of combination products, and lists helium leak, pressure or vacuum decay, dye ingress and mass-extraction tests for integrity of cartridges and prefilled syringes. No FDA device classification was found for an empty drug cartridge; pen injectors (code NSC) are Class II under 21 CFR 880.5860, and dental cartridge syringes are Class II and 510(k)-exempt, subject to stated limitations, under 21 CFR 872.6770. Humalog’s label (Warnings 5.1) states its cartridges must never be shared, even if the needle is changed.
