Ludwig-Maximilians-Universität Munich | KEN LO PRESTI, PHD-STUDENT

The residual moisture (RM) level strongly impacts the stability of freeze-dried biopharmaceuticals such as monoclonal antibodies. Thus, the RM of lyophilized products and its impact needs to be evaluated in development and stability testing. Specific RM adjustment is usually performed using open exposure in controlled low humidity chambers, by varying the freeze-drying cycle, or by pulling samples at different time points during freeze-drying. These methods are associated with little control over the RM. Recently, we published a technical note where we used Hamilton syringes to adjust the RM level of freeze-dried protein formulations very precisely.

Highly purified water was introduced into vials with lyophilized product at room temperature by pinching the needle through the flipped-off capped vial standing in an upright or horizontal position, ejecting the water droplet approx. 1 cm above the cake, and letting the droplet completely evaporate from the tip of the needle. It is important to note that water is not directly introduced into the cake, as otherwise, the cake could partially dissolve and the moisture inhomogeneous distribute. Instead, water vapor is formed which can diffuse into the cake. The rubber stopper may also be pre-pinched with an injection needle (20G x 1”) and the water droplet may be stripped onto the inner surface of the vial for a more efficient spiking throughput.

We used zero dead volume syringes and gastight syringes of the 7000 and 1700 needle series which allow highly reproducible water volume transfers of less than 1 µl and final RM contents below 0.5% depending on the mass of the lyo cake. Additionally; we showed that an even water distribution throughout lyo cakes of different densities and size resulted.

This RM modification by injection of well-controlled microliter volumes of water into the headspace above lyophilizates with Hamilton syringes can be performed independently after lyophilization; the methodology allows targeted adjustment of the RM for testing its impact on product stability.

The publication can be found in the European Journal of Pharmaceutics and Biopharmaceutics

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