Impact of spin-freezing parameters and excipient composition on product stability of a PEGylated peptide formulation

This study examines the impact of spin‑freezing parameters, as applied in continuous spin-freeze-drying processes, and formulation composition on the stability of a PEGylated peptide following freeze‑drying and storage. A trehalose‑based reference formulation was compared with two reformulated systems in which trehalose was replaced by either mannitol or a 75:25 sucrose-mannitol blend. Samples were processed under four distinct spin‑freezing conditions, varying in cooling and crystallization rates, followed by batch‑drying and storage at either 2-8 °C or 50 °C for up to 13 weeks. Product quality was evaluated by assessing peptide concentration, monomer content, and cake morphology. Across all formulations and storage conditions, variations in spin‑freezing parameters exhibited no consistent or statistically significant effect on peptide or monomer levels. In contrast, formulation composition emerged as the dominant stability determinant. Trehalose‑based samples maintained robust stability under both refrigerated storage and stress conditions, whereas mannitol‑based samples exhibited moderate degradation at elevated temperatures. The sucrose-mannitol formulation demonstrated pronounced instability at 50 °C, characterized by cake collapse, browning, and interference in peptide quantification, likely as a result of sucrose hydrolysis and the formation of aromatic degradation products. These findings highlight that, for the formulations investigated, the choice of excipient is critical for product stability and that systems susceptible to sugar degradation may require adapted analytical approaches, as well as optimized drying protocols and storage conditions.