A study highlighting low non-recoverable hold-up volumes using the manual drug product filtration system flow kits
Our manual drug product filtration system has been designed to minimize non-recoverable hold-up volumes, to increase process efficiency and cost-effectiveness.
In this study we outline how we measure and analyze the non-recoverable hold-up volume in manual drug product filtration system flow kits containing filters sized from < 1 inch (e.g., KA02) to 10 inches (e.g., NP6) positioning them in single and redundant filtration configurations.
Results confirmed the average non-recoverable hold-up volume, including inlet flow kit and excluding filter hold-up volumes, are:
- 55.9 g ± 4.0 g for KA02 single
- 72.7 g ± 8.8 g for NP6 redundant
Introduction
Final drug product filtration prior to filling is an essential step in drug product manufacturing. So, keeping non-recoverable volume as low as possible in this process, is key for maximizing yield and profitability.
Fig 1. Manual drug product filtration system in a redundant filtration set-up (two NP6 filters) equipped with an extra flush bag tray, Watson Marlow pump, and Palltronic Flowstar V with stand.
We designed this system with the intentional aim of reducing hold-up volume. Tubing length was reduced to the absolute minimum required, by utilizing movable valves, cascading filters positioned with a slight decline and a thoughtfully designed, compact layout, thereby reducing internal volume. Additionally, the system was designed with as few junctions as possible to lower the risk of product becoming caught in corners or dead zones. Where possible, tubing internal diameter was also reduced to allow effective air chasing, improving product recovery.
The flexibility of the system’s movable valve design allows positioning of filtration assemblies in either single or redundant configuration while accommodating multiple filter sizes within each configuration with consistent tubing hold-up. Minimal tubing variation between filter sizes ensures consistent tubing hold-up regardless of process variation with filter size.
Our study excludes filter hold-up volumes; flow-kit hold-up volumes were found to be relatively comparable across all single and redundant filtration manifolds. The specific manifolds used in this study can be considered broadly representative of a typical single and redundant configuration.
We tested the largest and smallest sizes, < 1 inch (e.g., KA02) and 10 inch (e.g., NP6) and both filter arrangements (single and redundant). Fluorodyne II DFL, a 0.2 µm rated polyvinylidene fluoride (pvdf) sterilizing-grade membrane was chosen as it is one of the most commonly used sterilizing-grade membranes for final sterile filtration of drug product.
Materials and methods
Table 1. Equipment used for this study
| Product code | Description |
| MANPUPSIT-EU | Manual drug product filtration system |
| MANPUPSIT-PUMP-EU | Peristaltic pump Watson Marlow 630 EU |
| FFS05R-LGR | Palltronic Flowstar V LGR filter integrity test instrument |
| MANPUPSIT-PLTFFS05 | Platform for the Palltronic Flowstar V or LGR filter integrity test instrument |
| AEDLGR020 | Air evacuation mat for a 20 L biocontainer bag |
We used single and redundant filtration flow kits for this study. Single filtration flow kits are used to process through a single sterilizing filter, while redundant filtration flow kits are used to process through two filters in series, providing an additional layer of assurance by verifying the integrity of each filter independently. FAT flow kits utilising MPX quick connects were used to allow ease of disassembly for hold-up calculations.
Table 2. Flow kits used for this study
| Product code | Description |
| X6090-2180LNS | PUPSIT NP6 FAT redundant |
| X6090-2180NNS | PUPSIT KA02 FAT single |
| X6090-2180PNS | PUPSIT inlet FAT system |
| X6090-2182PNS | PUPSIT 20 L flush FAT single |
The manual drug product filtration system incorporates six movable valves that can be manually removed and repositioned to accommodate a range of configurations.
Fig 2. Manual drug product filtration system shadowboard, displaying the three valve configurations based on filter size.
Our movable valves can be moved along the shadowboard (Fig 2) to accommodate small or large filter sizes. The three valve configurations for filter size positions are visually indicated using the three colors on the shadowboard:
- White (Path A) which supports filter sizes up to 2 inch
- Grey (Path B) which supports filter sized between 3 inch to 5 inch
- Black (Path C) which supports 10 inch filters
Each pathway supports both single and redundant configurations through movable valves. For this study, Path A single was used to install the KA02 single flow kit and Path C redundant was used for the NP6 redundant flow kit.
Non-recoverable hold-up volume testing
To ensure accurate assessment of non-recoverable hold-up, the flow kits were prepared and weighed in an identical manner for all six runs:
- The inlet flow kits were weighed on a balance dry in their ‘end’ state. All clamps were removed and the MPX blanks were attached at each connection point.
- The first filtration flow kits measurement was taken by weighing the full flow kit in their ‘end’ dry state. Clamps were placed upstream and downstream around each filter and the MPX blanks were attached at each connection point.
- The second measurement was taken by removing the filters from the flow kits and weighing each dry filter individually.
- The third measurement was taken by measuring the dry ‘end’ weight of the filtration flow kit without filters included.
To ensure the flow kits were in a process accurate end state to assess non-recoverable hold-up, a full process was completed using DI water:
- The first set of flow kits were installed. Six runs overall with new flow kits installed each time.
- Priming was conducted at 0.05 L/min for the KA02 filter and 0.1 L/min for the NP6 filter.
- Flushing was carried out for five min at 1 L/min for KA02 and 2 L/min for NP6, with three min directed to the flush bag and two min directed to the product outlet to ensure complete priming of the flow path.
- An air-chase through the inlet was performed at 0.5 L/min for 15 s or up to 0.3 bar (4.4 psi / 0.03 MPa) at the inlet pressure.
- A forward flow integrity test was then conducted at 2.76 bar (40 psi / 0.028 MPa) to confirm complete filter wetting and to simulate drain-down during recovery.
To ensure accurate non-recoverable hold-up volume could be calculated, key manual steps were performed identically at the end of each run:
- Containers were positioned beneath each disconnection point to capture and quantify any released fluid at these junctions.
- MPX blanks were replaced onto each of the flow kit connection points and clamps were placed upstream and downstream of each filter.
- The inlet flow kit was removed and weighed.
- The filtration flow kit was removed and weighed.
- The filters were removed and weighed separately. Any water released from the filters was also collected and weighed separately.
- The remaining flow kit excluding the filters was weighed.
- This was repeated for all six runs. To determine the non-recoverable hold-up, the dry weight was subtracted from the wet weight.
There are several process steps that can be implemented and are recommended to maximize product recovery. These include performing an air chase through the inlet and an optional blow-down step using the Palltronic Flowstar V. Together, these steps help recover as much product as possible through the filters and out of the outlet.
Table 3. Process step parameters
| Process step | KA02 Single | NP6 Redundant |
| Priming | 0.05 L/min | 0.1 L/min |
| Flushing | 1 L/min | 2 L/min |
| Inlet air chase | 0.5 L/min for 15 s or up to 0.3 bar at the inlet pressure | |
| Forward flow | 2.76 bar (40 psi / 0.028 MPa) | 2.76 bar (40 psi / 0.028 MPa) |
Table 4. Integrity testing parameters
| Process parameter | Value |
| Filter integrity test instrument | Palltronic Flowstar V |
| Filter wetting fluid | DI water |
| Test gas | Air |
| Forward flow filter integrity test pressure | 2760 mbar |
| Pre-stabilization pressure applied for KA02DFL | 2760 mbar |
| Pre-stabilization time applied for KA02DFL | 1200 s |
Results and discussion
Table 5. Summary of non-recoverable data for the manual drug product filtration system excluding filter hold-up
| Non-recoverable hold-up weight (g) | |||||
| Filter size | Configuration | Sample number | Inlet flow kit | Filtration flow kit | Total |
| KA02 | Single | 3 | 27.9 ± 0.9 | 27.4 ± 3.4 | 55.9 ± 4.0 |
| NP6 | Redundant | 3 | 21.7 ± 1.3 | 51.0 ± 7.6 | 72.7 ± 8.8 |
*For guidance on capsule non-recoverable volumes, contact your local MSAT representative.
In Figure 2, there are three valve configurations, each corresponding to different filter size options. The difference in tubing length and corresponding hold‑up volume between the smallest and largest filter sizes for each configuration, have been calculated and reported in Table 6. The movable valve design enables consistent hold-up volumes across these three valve configurations, allowing any filter size to be used without significantly increasing the measured volume for either single or redundant configuration. As demonstrated in Table 6, the difference between the smallest and largest filter sizes across both configurations is less than 10 mL. These values represent hold‑up volume, not non‑recoverable volume; therefore, in practical operating conditions, the true non‑recoverable volume is expected to be lower.
Table 6. Difference in volume in the tubing length between the largest and smallest filter sizes under each configuration
| Configuration | Difference in tubing length between smallest and largest filter size (cm) | Hold-up volume within this difference in tubing length (mL) |
| Single | 5 | 6.3 |
| Redundant | 7 | 8.9 |
The flexibility of the movable valves enables the use of both single and redundant filtration setups, as well as compatibility with filter sizes spanning from < 1 inch (e.g., KA02) to 10 inch (e.g., NP6), allowing full coverage across the required filtration range. The system maintains minimal tubing length across all configurations, resulting in a compact design irrespective of filter size or arrangement. In redundant filtration mode, a slight downwards slope is incorporated between filter 1 and filter 2 to promote directional drainage and maximize product recovery. Collectively, these design features minimize non-recoverable hold-up volume within the flow kit and support efficient recovery of the product feed.
It is worth noting that process variations during operation can significantly influence the observed non‑recoverable hold‑up volume. For example, if the inlet line is not air‑chased, additional residual fluid will remain upstream, increasing the measured hold‑up. Likewise, performing a filter blow‑down above the bubble point can force additional liquid through the filter housing and tubing, reducing the non‑recoverable volume. These operational differences highlight that hold‑up values can vary depending on user technique. For guidance on how these process variations may affect your setup, please contact your local MSAT representative for more support.
Conclusion
The non-recoverable tubing hold-up volume of our manual drug product filtration system, excluding filters, is less than 100 g across all single and redundant configurations.
We have optimized the manual drug product filtration system’s flow kit design and operation to enable efficient final sterile filtration of drug product. Maximizing product recovery relies on a combination of process steps and optimized flow kit configuration. Follow our recommended process step parameters (see Table 3) to achieve the same non-recoverable hold-up volumes.
Optional process steps such as performing an air chase through the inlet, along with an optional blow-down step using the Palltronic Flowstar integrity test instrument, support the efficient recovery of product through the filters and out of the outlet. In parallel, the flow kits themselves are engineered to reduce tubing lengths wherever possible, and to incorporate a slight decline that naturally promotes product movement across all filter sizes and configurations. Together, these design and process considerations help ensure that the highest possible product recovery is consistently achieved.
References
- Manual drug product filtration system Operating Instructions, Document number: 29806919, Revision AA
- USD2594(8a) – Instructions for Use Palltronic Flowstar IV LGR Instrument CY55987
CY59293