Crystallization Risk Assessment of Amorphous Solid Dispersions by Physical Shelf-Life Modeling: A Practical Approach

Amorphous solid dispersions (ASDs) of a poorly water-soluble active pharmaceutical ingredient (API) in a polymer matrix can enhance the water solubility and therefore generally improve the bioavailability of the API. Although examples of long-term stability are emerging in the literature, many ASD products are kinetically stabilized, and inhibition of crystallization of a drug substance within and beyond shelf life is still a matter of debate, since, in some cases, the formation of crystals may impact bioavailability. In this study, a risk assessment of API crystallization in packaged ASD drug products and a mitigation strategy are outlined. The risk of shelf-life crystallization and the respective mitigation steps are assigned for different drug product development scenarios and the scientific principles of each step are discussed. Ultimately, the physical stability of ASD drug products during shelf-life storage is modeled. The methodology is based on the quantification of crystal growth kinetics by transmission Raman spectroscopy (TRS), modeling the impact of water sorption on the glass-transition temperature of the ASD, and the prediction of moisture uptake by the packaged ASD drug product during storage. This approach is applied to an ASD of fenofibrate that features both fast API crystallization under accelerated storage conditions and long-term stability in a suitable protective packaging under conventional storage conditions.