Sterile filtration is employed at various stages of biopharmaceutical manufacturing, such as solution clarification, bioburden reduction, particulate removal, and mycoplasma reduction, prior to drug-product filling. It is particularly well-suited for products that are sensitive to heat or radiation.
These processes and products are susceptible to contamination by various adventitious agents, including bacteria, fungi, and viruses. These microorganisms possess the remarkable ability to adapt and thrive in diverse conditions. Consequently, such contamination poses significant risks to biologic products. It can lead to increased product variability, reduced potency due to microbial enzyme-driven degradation or modification, alterations in impurity profiles, and elevated bacterial endotoxin levels, as illustrated in Figure 1. Moreover, microbial contamination can result in prolonged shutdowns and manufacturing delays, necessitating thorough root-cause investigations and corrective actions. In some cases, these disruptions can even contribute to shortages of essential drug products. Given its profound impact on product safety and quality, it is imperative to maintain a focused effort on comprehending the underlying causes of microbial contamination and implementing effective measures to mitigate these risks in biologic product manufacturing.
Figure 1. Contamination product path.
Performing a hazard analysis and critical control point assessment during manufacturing helps establish a microbial control strategy and supports a thorough investigation.
Microbial contamination is more likely during upstream processing because nutrient-rich conditions promote microbial growth. In contrast, downstream biopharmaceutical purification processes usually operate under “low bioburden” conditions, where microbial levels are present but are routinely monitored and controlled, as illustrated in Figure 2.
Figure 2. Filtration of small molecule drug production, high risk components highlighted in red, low risk components highlighted in green.
Filter incompatibility—Selecting an appropriate filter or membrane is essential to achieving complete sterilization, including using a pore size suited to the organism of concern.
Defective filters—Cartridges can be damaged during shipment, installation, or operation, even when supplied as high-quality components. Minor openings, mechanical damage, pressure shocks, or exposure to unsuitable temperatures or chemicals can compromise filter integrity and lead to bioburden failures.
Clogging—Clogging is a common process-filtration challenge that can result from selecting a membrane with an inadequate pore size.
PUPSIT—Pre-use post-sterilization integrity testing verifies filter integrity after sterilization and before use. Steam sterilization can alter membrane porosity, potentially allowing particles of 0.2 µm or larger to pass through and cause contamination.
Assemblies—Missing or damaged O-rings or gaskets, incorrect filter assembly, post-sterilization filter deformation, or use of incorrect components can increase the risk of contamination.
Static systems—Limited fluid movement in process lines, particularly at junctions, can increase the risk of bacterial growth.
Bacterial type—Some microorganisms are deformable and, under high differential pressure or flow rates, may pass through filter pores that are only slightly smaller than the organism.
Filtration conditions—Elevated temperatures can reduce microbial retention when they decrease solution viscosity and increase flow rates.
Composition of the filtered solution—Solution composition and compatibility can adversely affect membrane-filter retention and integrity.
Sterilizing-grade filters should undergo integrity testing before and after processing to identify potential leaks and safeguard the product from defects stemming from compromised filters.
Use a validated sterilizing-grade filter to control the bioburden upstream. Filters used for final filtration must be validated to consistently remove microorganisms from the solution under the most challenging production conditions. Validation should involve a high bioburden challenge of at least 107 CFU/cm2 of effective filter area (EFA) and demonstrate that the challenge microorganism does not pass through the filter. Therefore, a validated sterilizing-grade filter should achieve a retention capacity of at least 7 LRV.
Refer to the sterilizing-grade membrane filter configurations recommended for each application.
|
Filter |
Configuration |
Application |
|
0.03 - 1.2 µm double layer sterilizing grade PES membrane (same pore size) |
Parenteral, cell culture media, buffers, serum, vaccines, biologics, and water for injection systems |
|
|
Prefilter PES pore sizes: 0.1 to 1.2 µm. Final layer PES pore sizes: 0.03 to 0.65 µm |
SVPs & LVPs, cell culture media, serum, vaccines, biologics, water purification and water for injection systems |
|
|
Double layer: Prefilter and asymmetric filter. 0.2/0.1, 0.5/0.2, 0.8/0.22 µm. |
High particle loads in cell culture media, serum, vaccines, biologics, and buffers |
|
|
Double layer PES positively charged 0.03, 0.1, 0.22, 0.45 µm |
Endotoxin removal in process water and water for injection systems |
|
|
PTFE 0.22 µm |
Tank vents, compressed air, pressurized gases, and fermentation air |
For additional information about sterilizing filters, refer to Buying Guide - BioPharmaceutical Applications.
A bioburden level above 10 CFU/100 mL in the unfiltered drug solution may not increase risk if effective sterilizing filtration is in place.
Filters with a 0.1 µm pore size can effectively remove mycoplasma.
Post-use integrity testing and upstream bioburden monitoring should be implemented to confirm filter effectiveness and prevent breakthrough.
Contamination can originate from many sources, including raw materials, facilities, equipment, personnel, processes, filters, and gases. A strong control strategy should account for each source when addressing the issue.
Critical Process Filtration’s Applications and Process Support staff are here to help you choose the right filter for your application. If you’re looking for a replacement for a sterilizing filter, we can recommend an appropriate equivalent. Our team can conduct any necessary testing to identify the best filters for your process and help you determine the number of filters needed for your specific application. We can also provide support in verifying and validating performance as required.
This article explores various aspects of a microbial control strategy, including recent cases of microbial contamination in specific biologic products. It emphasizes the importance of conducting periodic risk assessments and highlights additional areas for improvement in managing risks.