Evaluation of the accelerated stability of an allergen extract in combination with an inactivated bacterial suspension using the Advanced Kinetic Model (AKM)

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INTRODUCTION: The coadministration of allergen extracts with bacterial preparations has gained clinical relevance in subcutaneous immunotherapy for respiratory allergic diseases. However, there are no systematic studies evaluating the physicochemical stability or preservation of immunological activity of these mixtures. This study aimed to characterize the stability of a combined formulation using the Advanced Kinetic Model (AKM), a mathematical approach to shelf-life prediction based on nonlinear kinetics. METHODS: A lyophilized mite extract (D. pteronyssinus/D. farinae) and an inactivated bacterial suspension (IPI-Asac) were used. Incubations were performed at 4, 15, 30, 37, and 45°C for up to 90 days, with chromatographic (SEC-HPLC), electrophoretic (SDS-densitometric PAGE), and functional (ELISA-IgE) analyses. The samples were studied separately and in a 4:1 ratio (extract:bacteria). The AKM model was applied to the IgE-binding loss data to extrapolate long-term stability. RESULTS: No significant differences were observed between the extract alone and the mixture in terms of aggregation, protein degradation, or loss of IgE-binding capacity. At 15°C, >90% activity was retained for up to 90 days. Conclusion: The AKM model predicted a retention of 75% functional activity at 4°C for up to 1.5 years. The bacterial suspension did not alter the degradation kinetics or biophysical profiles. CONCLUSIONS: The data obtained suggest that the inclusion of an inactivated bacterial suspension does not compromise the conformational or functional stability of the allergens. The maintenance of IgE-specific activity under simulated storage conditions supports the technical feasibility of a coformulation. The application of the AKM model provided robust predictions of biological longevity without requiring prolonged stability studies under real-world conditions. The blending of allergenic extracts with inactivated bacterial suspensions preserves their immunological and biophysical properties under accelerated thermal conditions. These findings support the possibility of formulating combination products without negatively impacting immunotherapeutic efficacy, justifying additional clinical studies and multi-batch validation.

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