Supor™ Prime filter performance with high-risk fluids

Bacterial challenge testing of sterilizing-grade filters with high-risk fluids

The purpose of this study was to evaluate the performance of Supor™ Prime sterilizing-grade filters through bacterial challenge testing, using several complex fluids that represent a higher risk of bacterial penetration.

Supor™ Prime filter discs showed complete bacterial retention at both 0.34 bar (5 psid) and 2.76 bar (40 psid) with the four complex fluid types tested. These were:

• Lipid emulsion.
• Empty lipid nanoparticles.
• DNA-filled nanoparticles.
• Cholesterol-based liposomes.

Introduction

Although bacterial penetration of sterilizing-grade filters rarely occurs, it still remains an industry-wide challenge, with observations that some complex fluids (such as liposomes and emulsions) may lead to an increased incidence of penetration by Brevundimonas diminuta (B. diminuta) (1-4). Due to these observations, we developed several complex surrogate fluids to aid in the development of a new generation of Supor™ Prime filters that have shown improved performance with these challenging fluid types.

Our Supor™ Prime filters consist of a range of sterilizing-grade filters, designed for high throughput of high concentration biotech drugs and other challenging feeds.

Bacterial retention testing of sterilizing-grade filters consists of two types of challenge tests:

• Test 1: During sterilizing-grade filter development and manufacturing, filters are tested and validated using water or a buffer in accordance with the principles of ASTM F838 (5).
• Test 2: Prior to use of a final sterilizing-grade filter in a pharmaceutical process, it is necessary to perform a process-specific filter validation to demonstrate that the filter will perform as expected (1, 6, 7, 8). One aspect of this validation includes a bacterial retention test with B. diminuta under simulated process-specific conditions with actual product. This bacterial challenge must demonstrate complete retention of B. diminuta by the test filter when challenged with a minimum of 1 × 10⁷ colony forming units CFU/cm² effective filter area (EFA).

Appendix 1 highlights how validation of sterilizing-grade filters used for final sterile filtration of a drug product is a regulatory requirement.

Methods and materials

B. diminuta ATCC No. 19146 was used to conduct the bacterial challenge tests.

Filter discs were used for testing and were subjected to both pre- and post-challenge bubble-point tests as per standard procedure. All testing was performed in triplicate.

Test fluids:

1. Lipid emulsion, tested at 5 and 40 psid, with a volume throughput of 14.5 mL/cm² (equivalent to 145 L/m²).
2. Empty lipid nanoparticles tested at 2.1 bar (30 psid) with a volume throughput of either 5.1 mL/cm² (51 L/m²) or 14.5 mL/cm² (145 L/m²).
3. DNA-filled lipid nanoparticles tested at 30 psid with a volume throughput of either 5.1 mL/cm² (51 L/m²) or 14.5 mL/cm² (145 L/m²).
4. Cholesterol-based liposomes, tested at 5 and 40 psid with a volume throughput of 14.5 mL/cm² (145 L/m²).

The test filters were autoclaved at 121°C for 1 h. At least one 0.45 µm rated control filter was tested for each batch of challenge fluid to confirm the B. diminuta was appropriately sized and monodispersed.

Results and conclusion

Supor™ Prime filter discs showed complete retention with all fluids at both 5 and 40 psid and at all challenge volumes. These results assert the high performance of Supor™ Prime sterilizing-grade filters when used with complex and challenging process fluids, that can represent a higher risk for bacterial penetration.

The bacterial challenge test results show that Supor™ Prime filters are highly retentive when tested with these highly penetrative fluids, giving confidence for success with process specific filter validation in real-world applications.

Full results and test data are displayed in Tables 1 to 4 below.

Table 1. Results for bacterial retention testing of Supor™ Prime (0.2 µm rated) filters using a lipid emulsion (n = 3)

*1 bar = 14.5 psi = 0.1 MPa

Table 2. Results for bacterial retention testing of Supor™ Prime filter discs (0.2 µm rated) using an empty lipid nanoparticle at 2.1 bar (n = 3)

*1 bar = 14.5 psi = 0.1 MPa

Table 3. Results for bacterial retention testing of Supor™ Prime filter discs (0.2 µm rated) using DNA-filled lipid nanoparticles at 2.1 bar (n = 3)

*1 bar = 14.5 psi = 0.1 MPa

Table 4. Results for bacterial retention testing of Supor™ Prime (0.2 µm rated) filters using a liposome (n = 3)

*1 bar = 14.5 psi = 0.1 MPa