The solid‐state continuum: a perspective on the interrelationships between different solid‐state forms in drug substance and drug product

Objective The objective of the review is to provide an overview of the nomenclature used in the solid‐state continuum and relate these to the development of drug substances and drug products. Key findings The importance of a rational approach to solid‐state form selection, including integrated decision making (ensuring equal weight is given to the needs of the drug substance and the drug product), is vital for the effective development of a drug candidate. For example, how do secondary processing considerations influence the selection of drug substance solid‐state form and resulting formulation, and how can drug substance solid‐state form be used to optimise secondary processing? Further, the potential use of ‘crystal’ engineering to optimise stability, purity and optical resolutions, and the linked regulatory requirements, will be discussed. Summary The nomenclature used in the solid‐state continuum, which contains a large number of different crystalline and non‐crystalline forms, for example, amorphous systems, was reviewed. Further, the significant role of the drug substance within the solid oral dose form from a physicochemical perspective was covered.