Ensuring product stability – choosing the right excipients

The stability of pharmaceuticals is an important product quality attribute. Of the known factors affecting stability, moisture is often perceived as the most common cause of drug degradation by hydrolysis or other reactions facilitated by moisture as a medium. Excipients are a critical entity in formulations to enable drug delivery as well as efficient manufacture of pharmaceutical dosage forms. Yet to this end, there is limited application and understanding of the role of excipients in protecting moisture sensitive drugs. An improved understanding of moisture-excipient interactions is important when selecting excipients for formulations containing moisture sensitive drugs. This review outlines the role of excipients as a moisture protectant in oral solid dosage forms. It focuses on the moisture interactions of excipients in order to highlight the potential of certain excipients as moisture protectants. More specifically, the mechanisms by which excipients can reduce drug degradation (e.g. acting as a physical barrier, reducing moisture availability and mobility) are discussed. A summary of analytical tools to evaluate moisture-excipient interactions is also provided.