What characteristic is unique to a multi-dose vial?

The unique characteristic of a multi-dose vial is that it is typically good for a defined period, often 28 days, once opened. This timeframe allows for multiple uses of the vial while helping to ensure sterility and reduce the risk of contamination. The 28-day expiration is an important guideline to follow within pharmaceutical practices, as it balances safety and product usability after the initial opening.

In contrast, the durability of a multi-dose vial is not indefinite, which distinguishes it from other types of vials. Additionally, multi-dose vials commonly contain preservatives to extend their shelf life and maintain sterility, which would make the option stating the absence of preservatives incorrect. The storage conditions can vary; while some multi-dose vials are recommended to be stored at room temperature, others may need refrigeration. Therefore, the specificity of being good for 28 days after opening is what correctly identifies a multi-dose vial.