shelf life

Shelf life is how long a medicine stays good on the shelf — the window during which you can trust it to be as safe and effective as the day it was released. Like a best-before date on food, it is a promise tied to keeping the product in its proper packaging under stated conditions.

Formally, shelf life is the period over which a product remains within all of its specifications — drug content, degradation products, dissolution, appearance, microbial quality — when stored as directed. A common benchmark for chemical potency is the time for the drug to fall to 90 per cent of label claim (often written t90), though the binding limit may be a different attribute such as an impurity threshold.

Shelf life is established from stability studies: real-time data at the labelled storage condition, supported by accelerated data and Arrhenius modelling to project the answer before years have elapsed. The granted shelf life is usually conservative and is stated together with storage instructions, which together justify the printed expiry date.

An important caveat: shelf life applies only to the unopened product in its original container. Once a vial is broached, a syrup opened, or a powder reconstituted, a separate, much shorter in-use shelf life takes over, because exposure to air, water and microbes resets the clock.