Shelf-life estimation for multifactor stability studies

In stability analysis, the current Food and Drug Administration (FDA) recommended procedure for estimating the expiration dating period (shelf-life) of a drug is limited to a single package, single strength product. Since most drug products are manufactured with more than one strength and are marketed in more than one package, stability analyses must be carried out for every combination of package and/or strength. This paper proposes a generalization of the current FDA procedure to analyze the stability data from a multiple package and/or strength study. Monte Carlo simulation was used to address some issues with the current procedure and evaluate the proposed generalization procedure. The proposed procedure is illustrated by an application to a data set consisting of five batches and two packages. Statistical issues and problems with the current approach of concern to industrial statisticians and the generalization are also discussed.