Final sterile filtration operations are the focus of extensive regulatory guidance to assure the safety of medicinal products for administration to patients. All sterilizing-grade filters must be tested for integrity after use, and current draft EMA EU Annex 1 requires pre-use, post-sterilization integrity tests (PUPSIT). This poster explores the use of final fill filters to achieve the following: • Simplify PUPSIT by reducing risk of introducing microbial contaminants to the flow path • Maximize product recovery • Create a safer and more efficient final filtration process To learn more about this topic or collaborate with our technical experts, schedule an in-person or remote visit at our M Lab™ Collaboration Centers: www.merckmillipore.com/mlab

1. MerckMillipore.com
The life science business of Merck operates as MilliporeSigma in the U.S. and Canada.
Introduction
Final sterile filtration of formulated medicinal products is
performed late in production operations in a highly controlled
aseptic environment.
Final sterile filtration operations are the focus of extensive
regulatory guidance to assure the safety of these medicinal
products for administration to patients. All sterilizing-grade
filters must be tested for integrity after use, and current draft
EMA EU Annex 1 requires pre-use, post-sterilization integrity
tests (PUPSIT).
Millipak® Final Fill filters simplify PUPSIT by reducing the risk of
introducing microbial contaminants to the flow path: an aseptic
multi-purpose port (AMPP) provides a barrier between the
outside air and aseptic flow path during filter integrity testing.
While the selection of sterilizing-grade membranes is
traditionally based on performance, compatibility and quality,
filter format has a direct impact on the volume of product
recovered. Product retained by the membrane, support material,
and capsule is non-recoverable and is referred to as hold-up
volume. High hold-up volume has direct financial implications
due to the high value of final product.
This poster summarizes studies that confirm Millipak® Final Fill
filters maintain an aseptic flow path following multiple actuations
and demonstrates methods to maximize product recovery for
safer and more efficient final filtration processing.
Figure 1 Millipak® Final Fill Filters
Reducing Contamination
Risks
To assess the capability of the AMPP in preventing microbial
ingress, challenge testing was performed with Brevundimonas
diminuta (ATCC® 19146), the standard organism used for
sterilizing-grade filter retention testing.
Millipak® Final Fill Filters were gamma irradiated or gamma
irradiated followed by autoclaving. The AMPP was then
challenged with B. diminuta as indicated in Figure 2 and
actuated at least 18 times.
All tests were run in triplicate and included positive controls
(AMPP without O-rings) to confirm low levels of inoculum could
be detected, and negative controls (no microbial challenge) to
confirm the method could be run aseptically.
Figure 2. Summary of tests demonstrating microbial integrity of AMPP
following sterilization and actuations.
No microbial growth was detected in samples from any of the
test devices after challenge testing, confirming the AMPP
provides a barrier preventing bacteria from entering the flow
path during integrity testing and sampling.
Reducing Contamination Risk and Improving
Product Recovery During Final Sterile Filtration
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Lit. No. MK_PS4779EN Ver. 1.0 10/2019
Maximizing Product Recovery
For biopharmaceutical manufacturers, maximizing product recovery is
key to achieving process efficiency. The stacked disc format of Millipak®
Final Fill filters is designed to reduce hold-up volume as compared to
traditional pleated filters. However, incorporating a filter blow-down with
a short pressure hold at 20 psi above the filter’s bubble point
specification can further reduce the hold-up volume in the filter and
increase product recovery. Figure 3 shows the hold-up volumes of
pleated and stacked disc filters of different membrane areas containing
sterilizing-grade membrane following blow-down through the filter inlet.
Figure 3: Mean hold-up volume of pleated filters compared to Millipak® Final Fill
filters following a 1 minute blow-down with air through the filter inlet at 20 psi above the
filter’s bubble point specification.
After blow-down, the hold-up volumes of Millipak® Final Fill filters are
1.5-5 times lower than those of pleated filters across all filtration areas.
Reducing hold-up volume can impact the economics of filtration
operations, especially when considering larger area pleated filters.
Figure 4 illustrates potential revenue impact for products at different
price points when processed over pleated and stacked disc filters of
~1000 cm2. All costs are based on product recovery volumes following
blow-down with air through the filter inlet for 1 minute at 20 psi above
the filter’s bubble point specification.
Figure 4: Revenue impact to manufacturer for medicinal products at different price
points due to hold-up volume (after blow-down) in pleated filters and Millipak® Final Fill
200 filters containing Durapore® 0.22 µm membrane.
The economic benefit of reduced hold-up volume is highly dependent on
the dollar value of the products being processed. As the product price
increases, the benefit differential between filter formats also increases,
with the maximum benefit of the stacked disc filters aligning with high
price medicinal products.
Conclusions
Final sterile filtration operations are evolving with the development of filtration devices that meet the requirements of critical process steps
while providing sterility assurance and greater operational efficiency. Results presented here demonstrate that Millipak® Final Fill filters
offer several advantages for maintaining an aseptic flow path, maximizing product recovery, as well as streamlining mandatory integrity
testing operations. The advanced capabilities of the filter design simplify and improve process risk mitigation and yield, ensuring consistent
and reliable performance during final filtration.
Simplified Integrity Testing
and Product Recovery
Single-use systems are increasingly being adopted in final
filtration and the AMPP offers opportunities for a streamlined
single-use assembly design with fewer connections. Figure 5
illustrates a simplified design for performing integrity testing or
blow-down through the AMPP using automated integrity
testers.
Figure 5: System configuration for connecting automated integrity testers
to sterilizing-grade filters: A – connection through the filter inlet; B –
connection through the AMPP on Millipak® Final Fill filters.
Bubble point testing through the AMPP and inlet generate
equivalent bubble point values (data not shown).
In addition to the filter inlet, filter blow-down can be performed
through the AMPP using an automated tester to deliver a short,
elevated pressure hold. Using the AMPP, rather than the filter
inlet streamlines integrity testing operations by minimizing
contamination risks and reducing the number of connections
required. Figure 6 shows hold-up volumes of Millipak® Final Fill
200 filters following different drain and blow-down methods
through the filter inlet and AMPP.
Figure 6: Mean hold-up volume of Millipak® Final Fill 200 filters containing
sterilizing–grade Durapore® 0.22 µm membrane following gravity drain,
pressure increase to 55 psig (membrane’s bubble point) and a 1 minute
pressure hold to 70 psig (20 psi above the membrane’s bubble point) applied
through the filter inlet or AMPP.
Results confirm that filter hold-up volumes following elevated
pressure hold are similar, irrespective if the pressure is applied
through the inlet or the AMPP. Blow-down through the AMPP
with an automated tester at the membrane’s bubble point
pressure specification also reduces hold-up volume as
compared to gravity draining.
Using the AMPP to recover product from the filter with an
automated tester simplifies recovery, eliminating the need to
switch to a controlled pressurized gas source.
Ranjani Sundharam, An Son Leong, Lauren Kacmarcik, Andrew Koch
Merck, 80 Ashby Road, Bedford, MA 01730
A B
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Blow-down Method
Hold-upvolume(mL)
Hold-up of Millipak® Final Fill 200 Filters
Following Blow-down
Gravity Drain
Pressure increase to membrane BP through AMPP
Presssure through inlet to 20 psi above BP for 1 min
Pressure through AMPP to 20 psi above BP for 1 min