Unit dose or multidose: choosing a medicine's format
Eye drops are sold in a small bottle reopened for weeks, or in single-dose vials thrown away after use. The choice is not just a matter of marketing: it commits the formula, its preservation and its packaging.
By Tecmom editorial team · 2 min read
Two definitions
A single-dose container holds the quantity of a medicine intended to be given in one go. A multiple-dose container allows successive doses to be withdrawn without changing the safety, strength, quality or purity of what remains: that is, in substance, the definition in chapter 〈659〉 of the United States Pharmacopeia.
The difference looks arithmetical. It is above all microbiological: each opening of a multidose container is an opportunity for contamination.
What repeated opening requires
A multidose container must stay clean and stable from one opening to the next. Hence, in general, two requirements. The formula often contains an antimicrobial preservative, whose effectiveness is verified by testing. And the medicine is given an in-use shelf life, established by in-use stability studies, as European guidelines provide.
The packaging, for its part, must stay tight after dozens of openings and closings; see multidose sealing. For injectables, the US FDA even defines a multiple-dose container by the antimicrobial effectiveness tests it has passed.
What single dose brings, and what it costs
Opened only once, a single-dose container reduces the risk of contamination and may allow a preservative-free formula, sought after for some eye drops. It also guarantees an exact dose, with no measuring.
The trade-off is the amount of packaging: one container per dose, so more material and a higher cost per dose. The choice is therefore made product by product, between microbiological safety, ease of use, cost and environment.
On the farm, a different balance
In veterinary medicine, one bottle often treats several animals, and volumes range from millilitres to litres depending on the species. Multidose dominates there, with its sealing and handling requirements, often with gloves on; see packaging on the farm. The European Medicines Agency even has a guideline specific to in-use stability testing of veterinary medicines.
For eye drops, see the dropper bottle.
Single dose or multidose, the question is never just how many doses a bottle holds. It is what state the last one is in.
Glossary
- Single dose
- A container holding one dose, meant to be opened once.
- Multidose
- A container from which successive doses are withdrawn.
- Preservative
- A substance that limits the growth of micro-organisms after opening.
- In-use shelf life
- The period during which an opened medicine remains compliant.