Predicting stability of lyophilized products

The usual purpose of freeze-drying is to enhance the stability and thus the marketability of a product. Increasing the length of a product's integrity, however, often requires that the formulator be able to predict the extent of that increased shelf life. Based on the Arrhenius principles, techniques are available that can allow such shelf life estimates with an acceptable degree of confidence. The presentation reviews examples of ongoing studies demonstrating predictive techniques as applied to freeze-dried products. The examples cover the most common situations which call for straight-forward and generally accepted principles of prediction; that is, measuring a specific potency loss at several elevated temperatures and then predicting the time for the same loss at normal storage. Other situations, however, as is the case with many in vitro diagnostic products used in clinical laboratories, require a modification of this technique. In those instances, monitoring of the proper "functioning" of samples of a product subjected to exaggerated temperature conditions with an eye to predicting shelf life is reviewed.