Glass or plastic: what each material brings to a medicine
Glass was the first material of pharmacy bottles, and it remains that of injectables. Plastic has replaced it for a large share of syrups, drops and tablets. Neither has won: each has its own ground.
By Tecmom editorial team · 2 min read
What glass still does best
Glass is almost inert and impermeable: it lets through neither oxygen, nor water vapour, nor gases. It withstands the heat of sterilisation, can be cleaned and inspected by eye. For injectable medicines, sensitive and sterile, it remains the reference.
The European Pharmacopoeia distinguishes several types of glass. Type I, borosilicate glass, offers the highest hydrolytic resistance: it releases very few ions into an aqueous solution. Types II and III, soda-lime glass, suit other uses.
What glass costs
Glass breaks, and a shard on a filling line stops the whole line. It is heavy, which weighs on transport. Its shapes are more limited: a squeezable dropper bottle, pressed to dose, cannot be made of glass.
Even glass is not perfectly inert. Some solutions can, over time, tear fine flakes from its inner surface, a phenomenon known as delamination.
What plastic brings
Plastic is light and unbreakable. It can be moulded into complex shapes: droppers, squeezable bottles, hinged pill containers, child-resistant caps. For a syrup or a tablet, it reduces weight and breakage risk, at home as well as in the pharmacy.
In exchange, it is permeable: it lets a little gas and water vapour through, and can release substances into the contents or absorb them. Hence the studies of permeability and of extractables and leachables.
The choice depends on the dosage form
For an injectable, glass still dominates. For a syrup, PET has taken over, often in amber; see our article on amber bottles. For a multidose eye drop, soft plastic makes the measured drop possible.
Both materials can be tinted to filter light, and both are recycled. The question, then, is not which is better, but which best protects this medicine, in this use.
Glass protects better, plastic serves better. The right bottle is the one that does both well enough for the medicine it holds.
Glossary
- Type I glass
- Borosilicate glass with high hydrolytic resistance, used for injectables.
- Hydrolytic resistance
- A glass's ability not to release ions into an aqueous solution.
- Delamination
- The shedding of fine flakes from the inner surface of a glass container.
- Permeability
- The passage of gas or vapour through a wall.