Table II: Effects of vial size and dilution on reconstitution. FDS is formulated drug substance, WFI is water for injection.
Initial attempts to shorten the reconstitution by adding salt or surfactant to WFI were unsuccessful (data not shown), hence
other strategies were contemplated. First, using a larger vial (and therefore, a larger surface area) should reduce the reconstitution
time. Second, diluting the FDS before freeze-drying should reduce the reconstitution time, because Shire et al. showed that decreasing protein loading concentration resulted in a less dense cake that reconstituted more readily (1). When
six groups of samples with various vial sizes and FDS dilutions were freeze-dried in one cycle, the cake from the undiluted
FDS reconstituted faster when placed in a 50 mL vial (4.6 min) than it did in a 20 mL vial (6.4 min) (see Table II). Furthermore, the cake from the diluted FDS reconstituted significantly faster than that from the undiluted FDS, regardless
of the vial size employed.
However, combining both the larger vial with the FDS dilution provided no additive effect in reducing the reconstitution time.
The reconstitution time (~3 min) is essentially the same with either a 20-mL or a 50-mL vial at 2-fold dilution of the FDS.
Because of the higher production cost associated with a bigger (50 mL) vial (because fewer vials can be produced in a given
lyophilizer), the smaller (20 mL) vial with the diluted FDS was a viable scenario. The reconstituted time was reduced 37%
and 52% when the FDS was diluted 1.5-fold and 2-fold, respectively, in a 20-mL vial. To minimize the cycle length, a 1.6-fold
dilution of the FDS was chosen. This dilution would yield a solution containing 25 mg/mL FDS, which would substantially reduce
the original reconstitution time without necessitating a lengthy freeze-drying cycle.
Figure 1: Representative lyophilized vials from Table II.
To minimize changes in the manufacturing process of 40-mg/mL FDS at 5.5 mL-fill that had previously passed FDA inspection,
the 25-mg/mL FDS was manufactured by performing a 1.6-fold dilution of the existing 40-mg/mL FDS instead of being formulated
from scratch. Each vial was filled with 1.6-fold volume (5.5 x 1.6 = 8.8 mL) of the diluted FDS. After lyophilization, the
DP was reconstituted with the same volume of 2.3-mL WFI to yield the identical 80-mg/mL solution as the original process.
The DP from the 8.8-mL fill was referred as the tall cake, and that from the original 5.5-mL fill as the short cake (see Figure 1). The lyophilization cycle for the 40-mg/mL FDS was previously described. Following is the cycle development for the 25-mg/mL