Polymeric excipients for solid-state stabilization of protein formulations

Background Protein‑based therapeutics represent a substantial fraction of FDA‑approved biologics, and the continued expansion of protein modalities has increased the demand for effective stabilization strategies. Although solid‑state protein formulations generally offer superior storage stability compared to liquid formulations, drying processes such as lyophilization, spray drying, and spray freeze‑drying can introduce significant physical and chemical stresses that compromise protein stability. Area covered This review focuses on the role of high‑molecular‑weight polymeric excipients in the solid‑state stabilization of protein‑based injectable formulations. It discusses common sources of instability introduced during drying and long‑term storage, while summarizing and highlighting the growing interest in polymeric excipients as stabilizers. Mechanisms by which polymeric excipients enhance protein stability including amorphous matrix formation, reduced molecular mobility, and surface‑active protection against interfacial stresses are discussed. The regulatory status of polymeric excipients currently used in FDA‑approved injectables versus investigational materials is also considered. Expert opinion Polymeric excipients offer unique advantages for solid-state protein stabilization and may complement or surpass traditional low-molecular-weight stabilizers when rationally selected. However, broader adoption will require improved mechanistic understanding, careful consideration of excipient–protein interactions, and alignment with regulatory expectations. Continued development and systematic evaluation of polymeric excipients are expected to expand formulation design options and improve the stability and performance of next-generation protein therapeutics.