Ideally, all product formulations should experience the same conditions when it comes to lyophilisation as this leads to final product homogeneity. In practice, however, nucleation can occur. Nucleation is a random process and has proven difficult for the industry to control. During the freezing stage, some vials may nucleate close to the thermodynamic freezing point of the formulation (e.g., -3 ∘C), while others may nucleate at -20 ∘C or lower much later in the freezing step. Consequently, all the vials will behave somewhat differently because the temperature at which nucleation occurs ultimately determines the resistance to the water vapour flow out of the frozen sample during freeze drying. The lower the temperature when nucleation occurs, the longer the cycle time. Many other adverse effects have also been attributed to uncontrolled nucleation (Table I).
Mark Shon. VP of Sales and Marketing for SP Scientific.
A number of techniques for controlling nucleation have been previously described, including the ice fog technique and ultrasound.(1,2) One technique that could offer potential for controlling nucleation is a technology developed by Praxair Inc (ControLyo) that enables ‘nucleation on-demand’. The technique involves cooling vials to a temperature at which nucleation can occur and then pressurising the system with nitrogen or argon gas. The freeze dryer is then rapidly de-pressurized and all vials nucleate simultaneously. The benefits include reduced cycle times, improved homogeneity of product, less damage from freezing, reduced vial breakage and an overall process that is generally more in conformity with quality by design initiatives. In addition, the technology is repeatable, scalable and has a large body of documented experimental data to validate its efficacy and benefits.(3)
In the initial work conducted by Praxair, they demonstrated controlled nucleation in freeze dryers as large as 5 m2. In a drying time optimisation experiment conducted by Praxair in collaboration with Baxter BioPharma Solutions, primary drying time was reduced 41% in the controlled compared with the uncontrolled nucleation run.3 Given the cost of freeze drying, cycle time reduction is a critical goal in the industry. Praxair has now implemented the technology on larger production freeze dryers. The hurdle is probably not the scalability of the technology, but the time and cost of a manufacturer having to revalidate an entire process once the technology has been incorporated. Because of this, the technology may be more practical for a new drug formulation where validation has yet to be performed.
Table 1: The effects of uncontrolled nucleation.
There is significant data that clearly show the benefits of controlled nucleation,4 but most of these have been generated using development freeze dryers. The real commercial benefit of any technology will come when it is adapted for production freeze dryers. Controlling nucleation will also benefit biological products. We have conducted work with lactate dehydrogenase and human growth hormone, which are both sensitive proteins. Controlled nucleation led to less protein aggregation and greater stability and function of the proteins after lyophilisation.
1. S. Rhambhatla et al., AAPS Pharm. Sci. Tech., 5(4), e58 (2004).
2. A. Hottot, K. Nakagawa and J. Andrieu, Chemical Engineering Research and Design, 86(2), 193–200 (2008).
Data held on file at Praxair and SP Scientific.
4. R. Sever, CPPR Freeze-Drying of Pharmaceuticals and Biologicals Conference (Garmisch, Germany, 2010).