Residual moisture is a common reactant that promotes degradation reactions leading to insufficient storage stability or shelf-life of a lyophilized product. Additionally, the mechanism by which the drug molecules are stabilized in the lyophilized state is attributed to the formation of highly viscous amorphous glassy states with low molecular mobilities and low reactivities. The glassy/amorphous state is characterized by glass transition temperature, and Tg and Tg values are impacted by water which acts as a plasticizer. Hence, it is important that systematic studies be performed to determine the acceptable levels of residual moisture in the product by exposing the lyophilized product to various levels of moisture content, time, and temperature. Since water also ingresses into the product from stoppers over the period of time, residual water in the stoppers after processing should also be determined. This chapter describes various methods that are commonly used to determine the residual moisture in the stoppers and lyophilized cake, and how to set moisture specifications is illustrated with an example.

Design of Moisture Specification Studies for Lyophilized Product

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