Robustness testing in pharmaceutical freeze-drying: Inter-relation of process conditions and product quality attributes studied for a vaccine formulation

Abstract

Context: The recent US Food and Drug Administration (FDA) legislation has introduced the evaluation of the Design Space of critical process parameters in manufacturing processes. In freeze-drying, a “formulation” is expected to be robust when minor deviations of the product temperature do not negatively affect the final product quality attributes.

Objective: To evaluate “formulation” robustness by investigating the effect of elevated product temperature on product quality using a bacterial vaccine solution.

Materials and methods: The vaccine solution was characterized by freeze-dry microscopy to determine the critical formulation temperature. A conservative cycle was developed using the SMART™ mode of a Lyostar II freeze dryer. Product temperature was elevated to imitate intermediate and aggressive cycle conditions. The final product was analyzed using X-ray powder diffraction (XRPD), scanning electron microscopy (SEM), Karl Fischer, and modulated differential scanning calorimetry (MDSC), and the life cell count (LCC) during accelerated stability testing. Results: The cakes processed at intermediate and aggressive conditions displayed larger pores with microcollapse of walls and stronger loss in LCC than the conservatively processed product, especially during stability testing. For all process conditions, a loss of the majority of cells was observed during storage.

Conclusion: For freeze-drying of life bacterial vaccine solutions, the product temperature profile during primary drying appeared to be inter-related to product quality attributes.

Keywords::

• Freeze-drying
• lyophilization
• Process Analytical Technology
• process robustness
• Quality by Design
• manometric temperature measurements

Acknowledgments

Susanne Hibler is gratefully acknowledged for the collapse temperature determination of the vaccine formulation via freeze-dry microscopy. The stability testing department at IDT Biologika is acknowledged for performance of the life cell counts and accelerated stability tests.

Declaration of interest

The authors report no conflicts of interest. The authors are solely responsible for the content and writing of the paper.