Why Glass Ampoules Are Important for Sterile Drug Packaging

Injectable drugs may be stored for up to two to three years. During this time, they must remain sterile and not be chemically altered by the primary container. An ampoule has a basic structure to enable this. It consists of a glass body with an open neck used to fill the drug solution and the neck is flame-sealed. Because they use no rubber or plastic in the seal, are still preferred, as they can store a sterile single dose.

How an Ampoule Is Made and Sealed

Pharmaceutical ampoules are formed from borosilicate glass tubing. The tubing is heated, shaped into a body and a narrow stem, and cut to length, with standard dimensions set out in ISO 9187-1. Operators fill the drug through the open stem. For oxygen-sensitive products, operators usually purge the headspace with nitrogen before sealing. Most production lines use pull sealing, in which the top of the stem is drawn away as the glass melts. This method creates a stronger, more uniform seal than melting the tip alone.

To allow controlled opening, the neck is weakened at the factory by one of two methods:

• a one-point cut (OPC), identified by a coloured dot above the score line
• a ceramic break ring printed around the neck

Both methods allow the neck to break cleanly under moderate pressure, which reduces the risk of injury to the user.

Why Borosilicate Glass Is Used

Injections require glass that will not interact with the product. Pharmaceutical glass can be classified based on its water resistance (USP <660>). Type I borosilicate glass has the highest water resistance. This means very little alkali will leach into solution and therefore the pH and formulation are stable during the shelf life. Ampoules made from type I glass can be purchased in sizes between 1 ml and 50 ml from manufacturers such as Borosil Scientific.

Borosilicate glass has a low coefficient of linear expansion, meaning it is commonly used in laboratory apparatus like . This is due to the fact that it will undergo many cycles of heating and cooling. The low coefficient of linear expansion means that the ampoule can withstand the high temperature of flame sealing and sterilising in an autoclave (121°C) without cracking.

How Ampoules Protect the Drug

A fused glass seal provides complete closure. This offers several practical benefits:

• Microbial protection, as there is no gap through which micro-organisms can enter
• Moisture and oxygen protection, since neither passes through glass
• Tamper evidence, as an opened ampoule cannot be resealed
• Visual inspection, as clear glass allows particles or discolouration to be detected before use

One limitation should be noted. Breaking the neck can release small glass fragments into the solution, and many hospitals therefore draw up ampoule doses through a filter needle or filter straw.

Ampoule or Vial?

The vial itself is made of the same type (I) glass. The main consideration comes down to the closure and number of doses needed. A rubber stopper allows multiple punctures, thus making it suitable for multi-dose products. It, however, introduces a second substance into contact with the drug. Some formulations take up extractables from rubber, while others lose active ingredient through adsorption onto the stopper. In such cases, an ampoule is generally the more suitable container.

Where Ampoules Are Used

Ampoules are best suited to small volumes of sterile liquid administered as a single dose. Typical applications include:

• injectable medicines, including local anaesthetics and emergency drugs
• water for injection and other diluents
• certain vaccines and biological products
• diagnostic reagents
• certified reference standards for analytical testing

In each case, the product must reach the patient or laboratory exactly as it was filled.

Choosing the Right Ampoule

Decisions made at the specification stage have a direct effect on filling performance. The main factors to confirm are:

• Glass type: Type I borosilicate for all parenteral products
• Capacity: sufficient volume for the full dose plus headspace, as liquid on the neck can weaken the seal
• Colour: amber glass for light-sensitive drugs
• Dimensions: close tolerances on stem diameter and wall thickness to prevent breakage on high-speed lines

Agreeing these points with the glass supplier before filling trials avoids costly changes later.

Conclusion

The ampoule has been used in the pharmaceutical industry for over a century. It remains a strong choice for its intended purpose. The sealed glass provides a sterile, stable, and visible single dose. The glass ampoule remains a trusted and popular choice for single-dose injectable applications. With careful consideration given to glass type, fill volume, colour and size, protection can be provided from the fill line to the patient.