Perspective on the influence of suspension manufacturing unit operations on bioburden viability and selection of sampling points at the pilot scale

The suspension wet media milling manufacturing process is a complex multi-unit operation, resulting in drug substance comminution to a target particle size. As a result of this complexity, microbial contamination is of paramount concern, particularly for suspensions dosed for parenteral use. This perspective sought to review the influence of (4) critical manufacturing unit operations using a quality risk management approach to better identify and articulate impact of each unit operation on bioburden viability. The manufacturing unit operations in scope included slurry compounding, deaeration, milling, and filling. Bow tie risk analysis was used as a visual gap analysis tool to evaluate if conventional controls were appropriate to detect and mitigate potential for microbial contamination. A deep dive into these unit operations clarified that mechanisms such as turbohypobiosis, cavitation during deaeration, high energy milling, and inert overlay may have an appreciable influence on bioburden viability and proliferation. The resultant analysis also explicated that endotoxin oversight must be closely monitored through barriers (input material controls, water quality controls) to minimize impact to the product and patient. The identified manufacturing unit operations were not appropriate as mitigating controls for endotoxin. The output of this article relates risk intersections for microbial contamination during wet media milling and offers insights in critical areas for intervention.