(M1230-11-60) The Effect of Conventional Cooling Versus Controlled Ice Nucleation on Primary Drying Time

Purpose: The purpose of this study was to contrast and compare conventional cooling and controlled ice nucleation using rapid depressurization on the primary drying time of common excipient formulations.

Methods: Two excipient formulations were used during the study.  One contained 5% W/V sucrose in water and the second contained a mixture of 3% W/V sucrose with 3% W/V mannitol in water.  The solutions were prepared at 2L, mixed well to dissolve, and filtered through bottle-top, vacuum filtration systems equipped with 0.2 micron nominal pore size PES filters. The solutions were transferred into 10 mL glass, tubing vials using a peristaltic pump to deliver 5 mL per vial.  Each lyophilization cycle used an entire tray that consisted of approximately 230 vials.  Stoppers were partially seated on the vials prior to transferring them to the lyophilizer.  Each tray was equipped with 1 vial located in the front and back with thermocouples and 2 to 3 vials located in the center of the tray with thermocouples.  The primary drying step for each formulation was designed to maintain the highest product temperature without evidence of failure.  Failure was defined as changes to the appearance of the lyophilized solid that resulted from exceeding the acceptable product temperature.  The product temperatures were maintained less than -33^oC for the 5% sucrose formulation and less than -16^oC for the sucrose / mannitol formulation. The conventional cycle used a cooling rate of 1^oC/min to -40^oC with a 2 hour hold at -40^oC before initiating primary drying.  The cycle using controlled ice nucleation cooled the samples to -5^oC and equilibrated them at that temperature with a pressure of 28 PSI for 90 minutes before rapidly releasing the pressure and cooling to -40^oC at 0.25^oC/min to allow for adequate ice crystal growth.  The sucrose / mannitol formulation used a conventional cycle with an annealing step at -15^oC to encourage crystallization of mannitol, but an annealing step was not used for the controlled ice nucleation cycle. Lyophilized solids were examined using modulated differential scanning calorimetry to examine them for changes in Tg and any evidence of crystallization of mannitol.  X-ray powder diffraction was used to examine solids for crystallinity.

Results: The product temperature at which failure was observed was identified for each formulation using freeze-dry microscopy and during primary drying.  Shrinking is common for amorphous formulations, such as 5% sucrose, but increases in shrinking were observed when the product temperature was warmer than -33^oC.  A conventional primary drying cycle required a shelf temperature of -25^oC with a chamber pressure of 100 mTorr to maintain the product temperature of -33^oC.  Controlling ice nucleation at -5^oC required a shelf temperature of -21^oC with a chamber pressure of 100 mTorr to maintain a product temperature of -34^oC.  Controlling ice nucleation at -5^oC reduced the overall cycle time by 25 hours for the 5% sucrose formulation. Poor appearance of the 3% sucrose with 3% mannitol formulation was observed when the product temperature was warmer than -21^oC.  A conventional primary drying cycle utilized an annealing step at -15^oC to encourage crystallization of mannitol, followed by primary drying using a shelf temperature of +30^oC with a chamber pressure of 100 mTorr to maintain the product temperature at -21^oC.  Controlling ice nucleation at -5^oC eliminated the need for an annealing step.  Primary drying was conducted using a shelf temperature of +30^oC with a chamber pressure of 100 mTorr to maintain the product temperature at -24^oC.  Controlling ice nucleation at -5^oC reduced the total cycle time for the 3% sucrose with 3% mannitol formulation by 7 hours.

Conclusion: An amorphous formulation containing 5% W/V sucrose was lyophilized using a conventional lyophilization cycle designed to maintain the product temperature at -33^oC to produce solids with pharmaceutically acceptable appearance. The total cycle time was 95 hours.  The same formulation was lyophilized after controlling ice nucleation at -5^oC and the total cycle time was reduced by 25 hours while maintaining solids with pharmaceutically acceptable appearance. A second formulation containing 3% W/V sucrose with 3% W/V mannitol was annealed at -15^oC to encourage crystallization of mannitol and lyophilized using a conventional cycle that maintained the product temperature at -21^oC to produce solids with pharmaceutically acceptable appearance.  The total cycle time was 37 hours.  The same formulation was lyophilized after controlling ice nucleation at -5^oC.  The cycle did not require an annealing step to ensure crystallization of mannitol and all solids exhibited pharmaceutically acceptable appearance.  The total cycle time was reduced by 7 hours.

References: R. Geidobler and G. Winter, "Controlled Ice Nucleation in the Field of Freeze-Drying: Fundamentals and Technology Review," European Journal of Pharmaceutics and Biopharmaceutics, 85, 2013, 214-222.
James a. Searles, John F. Carpenter, and Theodore W. Randolph, "the Ice Nucleation temperature Determines the Primary Drying Rate of Lyophilization for Samples Frozen on a Temperature-Controlled Shelf," Journal of Pharmaceutical Sciences, 90, 7, July 2001, 860-871.
Julian H. Gitter, Raimund Geidobler, Ingo Presser, and Gerhard Winter, "A Comparison of Controlled Ice Nucleation Techniques for Freeze Drying of a Therapeutic Antibody," Journal of Pharmaceutical Sciences, 7, 11, May 2018, 2748-2754.


Table I. Comparison of Lyophilization Cycle Conditions for 5% W/V Sucrose .


Table II. Comparison of Lyophilization Cycle Conditions for a 3% W/V Sucrose with 3% W/V Mannitol Formulation


Figure 1. In-Process Lyophilization Cycle Data for 3% Sucrose with 3% Mannitol Using Controlled Ice Nucleation at -5C and Primary Drying at +30C.