Sterilisation methods for single use medical consumables and the evidence behind them

A box of sterile syringes or catheters carries a short line on its label naming how it was sterilised. Most buyers read past it, yet it points to one of the largest bodies of evidence behind the product, and to the records that show whether your batch was treated the way the product was validated.

This article describes general practice. Which methods are accepted, which standards apply and what a regulator expects to see are set by each market and by the type and risk class of the product. Check the current requirements for your own market before relying on any summary, including this one.

How are single use medical consumables sterilised?

Single use consumables are almost always sterilised in their final packaging, at the end of manufacture, by a process chosen to suit the materials of the product and its pack. A small number of methods account for most of what is on the market.

Ethylene oxide

Ethylene oxide is a gas that kills microorganisms at moderate temperatures, which is why it suits heat sensitive plastics, complex assemblies and narrow channels such as catheters. The gas has to reach every surface through the packaging, so the pack must be breathable. After exposure the product needs aeration to remove residual gas and its by products, and the manufacturer must show that what remains is low enough to be safe for the patient.

Radiation: gamma, electron beam and X-ray

Radiation sterilisation passes energy through the sealed product. Gamma penetrates deeply and suits dense cartons. Electron beam is fast but penetrates less, so it suits lighter products and smaller packs. Radiation leaves no chemical residue, but it can make some polymers brittle or discoloured over time, so material compatibility and ageing studies matter more here than with gas.

Steam and other methods

Steam under pressure is well understood and leaves no residue, but many single use plastics cannot tolerate it, so it is more common for metal instruments, textiles and solutions. Low temperature methods such as hydrogen peroxide serve particular products, each with its own validation logic.

How is a sterilisation process validated?

A product cannot be tested into sterility. A sample test says little about the units that were not tested, so the evidence must come from proving that the process works, every time, for that product in that pack.

In broad terms, validation covers four things. First, the manufacturer shows that the product and its pack tolerate the process without losing function or safety. Second, the natural microbial load on the product before sterilisation, called bioburden, is measured, because the process is designed to overcome it. Third, the process is qualified: the equipment is shown to work as specified, and the product is shown to receive the intended treatment in every part of a realistic load. Fourth, the manufacturer demonstrates that the process reaches a defined sterility assurance level, which is the very small probability that any single unit is still not sterile.

Each method is governed by its own international standard: for ethylene oxide, radiation and moist heat, these are the ISO 11135, ISO 11137 and ISO 17665 series respectively, and packaging for terminally sterilised products falls under the ISO 11607 series. Ask which edition the validation was performed against.

What evidence proves that each batch was sterilised?

Once a process is validated, every batch is released against routine records showing it ran within its validated range. Those records depend on the method.

• For radiation, dosimeters placed in the load record the dose actually delivered, and release is based on those readings falling inside the validated range.
• For ethylene oxide, release is based on the recorded cycle parameters, and often on biological indicators placed in the load and then incubated to show that test organisms were killed.
• For steam, the cycle record of temperature, pressure and time, with any indicators used, plays the same role.

A batch certificate or certificate of conformance for a sterile product should name the sterilisation method, the sterilisation lot or cycle reference, and the facility that carried it out. Our article on the certificate of analysis and certificate of conformance explains what each kind of certificate can and cannot prove.

Why does the packaging matter as much as the process?

Sterility only lasts as long as the sterile barrier around the product stays intact. The pack must let the sterilant in where needed, survive the process, and then keep microorganisms out through transport, storage and handling until the point of use. Packaging validation, seal integrity testing, transport simulation and ageing studies are therefore part of the sterilisation evidence, and the printed shelf life rests on them. A crushed carton or a damaged pouch on arrival is a sterility question, not only a cosmetic one, as our article on incoming goods inspection explains.

What should a buyer ask a supplier for?

The validation itself sits in the manufacturer's technical file and will not be released in full. A reasonable request includes:

• the sterilisation method and the standard and edition the process was validated against;
• the name and location of the sterilisation facility, which may be a contract sterilisation site rather than the factory itself;
• a summary or certificate of the validation, and the date of the most recent revalidation or periodic review;
• for ethylene oxide, confirmation that residue testing was performed and passed;
• the packaging validation summary and the basis for the stated shelf life;
• the routine release record or certificate for your batch.

What are the warning signs?

A few patterns are worth stopping for. A sterilisation certificate that names a different product family, pack configuration or facility from the one you are buying. A validation that predates a change of material, supplier or pack, with no record that the change was assessed. Batch certificates that state the product is sterile but give no sterilisation lot or method. Shelf life claims with no ageing study behind them. And a supplier who cannot say where the product was sterilised at all. None proves the product unsafe, but each is a gap your regulator will eventually ask about.

For the range of single use products we source, see medical consumables. For the wider documentation pack behind a device, see what a medical device technical file contains, and for checking a delivery on arrival, incoming goods inspection.

NJMC Medical Supplies Co., Ltd is a trading and consultancy company in Nanjing, China, supplying medical equipment, medical consumables and active pharmaceutical ingredients to healthcare institutions, sourced from manufacturers in China and India.

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