(M1230-02-13) Mechanistic Understanding of Sodium Metabisulfite-Induced Drug Degradation: An Interplay of In Silico and Experimental Studies

Purpose: During the stability evaluation of an oral solution formulation containing sodium metabisulfite as an antioxidant, the formation of a previously unreported degradant was observed. The degradant was observed during storage, and understanding its identity was required to support hazard assessment for drug product development.

Methods: Comprehensive studies, including chemical stress, isolation, and structural elucidation, were conducted: 1) In silico prediction of the degradation pathway was explored; The drug substance was stressed under chemical conditions to enrich the degradant from ~0.05% to ~5%; The enriched degradant was isolated with prep-HPLC and SPE; The isolated degradant was characterized with LC-MSⁿ and 1D/2D NMR; The toxicity and stability of the degradant were evaluated:1) The characterized degradant raised genotoxicity concerns and was assessed by in silico methods; 2) The degradant was synthesized for the AMES assay test; 3) Its in vitro stability was also investigated in FaSSGF and FeSSIF solutions by LC-MS.

Results: This degradant is a covalent adduct between the active pharmaceutical ingredient (API) and bisulfite, which is a novel structure. The adduct formation was found to be specific to aqueous environments in the presence of metabisulfite under storage and stress conditions. The degradant was proposed to be formed via a mechanism that's not archived in current in silico prediction software. The degradant was found to be more stable in acidic conditions, as in the oral formulation, than in neutral conditions. The degradant was alerted as positive by in silico genotoxicity screening, but the AMES assay result indicated negative genotoxicity. 

Conclusion: In silico degradation pathway prediction did not suggest the formation of this adduct, suggesting a novel reaction mechanism not currently captured in existing degradation databases (Figure 1). This finding underscores the limitations of predictive tools when faced with unique drug–exipient interactions. Similar adduct structures were generated and characterized for several analogues, highlighting the importance of experimental validation. Our study provides structural insights into the degradant structure and degradation mechanism, demonstrating the need for comprehensive degradant profiling in solution-based dosage forms, especially when reactive excipients such as bisulfite salts are involved. This informs strategic decision-making for formulation design, regulatory risk assessment, and quality control.

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