Robust Process Scale-Up Leveraging Design of Experiments to Map Active Pharmaceutical Ingredient Humid Drying Parameter Space

Sugammadex is a modified γ-cyclodextrin active pharmaceutical ingredient (API) that is used as a reversal agent for neuromuscular blockade drugs in general anesthesia. The open structure of the cyclodextrin molecule yields a multitude of solid forms, and to date, more than 12 different mixed methanol solvate/hydrate forms have been characterized. Historically, the kinetic form (type 1) was manufactured to ensure that the solids could be dried successfully using only heat and vacuum to meet the specifications for residual solvents. Isolation of the thermodynamic form (type 2) was avoided due to the inability to remove process solvents to desired levels during drying and the subsequent need to rework the solids. To meet increasing product demand through improved robustness, the process was redesigned to manufacture the thermodynamic form (type 2). Therefore, an improved drying process had to be developed to enable meeting residual solvent levels of the final API at a large scale. Small-scale drying experiments were performed using a custom, in-house, process analytical technology-enabled drying platform to visualize the real-time evolution of the process solvents and water from the solids and to monitor form change. The mechanism for solvent removal in this case was found to be unique since it was independent of API crystallinity. The key element for successful drying was the displacement of solvent by water molecules, regardless of whether the crystal structure remained intact or collapsed. A predictive model was developed through design of experiments including three-factor interactions of drying humidity, temperature, and pressure, and the model was used to define the operating space to ensure successful drying. The humid drying conditions identified in this study were implemented across scales to ensure that residual solvent specifications were achieved regardless of the crystalline form generated.