Stability studies are typically conducted for products which degrade, or may degrade, but they may not be done for other medical devices.
A stability study typically evaluates the product at various time points to ensure the product is still functioning properly over the intended life of the product.
Shelf Life
If the product has a specific shelf-life, it will need a study to validate that it is good over that entire shelf life. A study is designed and executed over the intended life of the product and beyond.
Typically, at least three lots are put on study and the studies last for years (as the desired shelf-life is typically at least several years).
Time Points
The product is tested at various time points, typically 0, 3, 6, 9, 12 18, 24 months and then 12 month increments beyond 24 months.
The data for all lots tested is pooled and a regression analysis performed to evaluate the product for degradation and sometimes to predict the possible failure point.
Using multiple lots of product allows a confidence limit to be established and therefore the expected shelf-life can be stated with the desired level of confidence.