Quantifying the effect of particulate impurities on the ice nucleation behavior of pharmaceutical solutions

Numerous commercially available biopharmaceuticals are frozen or freeze-dried in vials. The temperature at which ice nucleates and its distribution across vials in a batch is critical to the design of freezing and freeze-drying processes. Here we study experimentally how the level of particulate impurities - a key parameter in pharmaceutical manufacturing - affects the ice nucleation behavior. Samples prepared under particulate-free conditions were found to nucleate at significantly lower temperatures and with more variability than samples of the same composition that were prepared under standard laboratory conditions, i.e., without using any means of lowering particulate counts. In contrast, spiking solutions with silver iodide particles resulted in significantly higher and less variable nucleation temperatures. These findings confirm that the level of particulates has a relevant effect on the rate of ice nucleation under conditions of industrial relevance. We further assessed the nucleation behavior of two biopharmaceuticals, a vaccine based on a viral vector and a mAb, and observed major differences in their nucleation behavior. This emphasizes the importance of measuring the ice nucleation behavior of biopharmaceuticals during process design.