The increasing application of single-use components and systems in bioprocessing represents one of the most significant changes in biopharmaceutical manufacturing in recent times. Driven by various factors such as improved efficiency, flexibility, and economics, this trend also presents specific challenges to end users. In one industry review by Langer, extractables and leachable compounds from disposable components were considered by end users to be a major area of potential concern regarding safety, efficacy, and stability of the pharmaceutical product (1). In a more recent survey by the Bio-Process Systems Alliance (BPSA), however, extractables and leachable compounds were considered by only 13% of respondents to be a barrier in integrating single-use technologies into existing or new processes (2). The apparent change in thinking may be due, in part, to an increased amount of information available in published case studies, reviews, and industry guides such as those issued by BPSA (3,4) covering regulatory issues, risk assessment, and test programs.

PRODUCT FOCUS: ALL BIOLOGICS

PROCESS FOCUS: UPSTREAM AND DOWNSTREAM PROCESSING

WHO SHOULD READ: PRODUCT/PROCESS DEVELOPMENT QA/QC, AND ANALYTICAL

KEYWORDS: ANALYTICAL METHODS, PROCESS VALIDATION, DISPOSABLES

LEVEL: INTERMEDIATE

Extractables are typically determined with laboratory tests using standard extraction fluids termed model solvents. Such tests are designed to exceed worst-case product and process conditions and reveal chemical entities that may migrate from process components into the final product as potential leachables.

The quality and quantity of materials extracted from an organic polymer component depends not only on the materials of construction, but also on the contact fluid composition, temperature, contact area, and contact time. In a multicomponent single-use system, the importance of each parameter in the migration of potential leachable compounds will vary according to component type and process conditions. For example, a sterile connector may have only transient exposure to a fluid during transfer, whereas a flexible biocontainer may be in contact with product or process fluid for many hours, days, or even months. Similarly, a typical small capsule filter with an effective filtration area of 0.15 m² may have an internal surface area of ~150 m² compared with a 0.5-L flexible biocontainer with a surface area of only 0.05 m² — 3,000× smaller. For these reasons, extractables studies should be designed and performed under conditions appropriate for each specific component and process application. That can provide an accurate and suitable assessment of the potential for the component or system, to release leachables into the drug product.

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We applied this customized approach to two previous studies on extractables In the first study, we reported extractables results from tests on sterile connectors and membrane filter capsules (5). The test articles were preconditioned by gamma irradiation at 50 kGy to represent worst-case sterilization conditions and extracted under exaggerated simulated conditions using a recirculating system with extraction times of four hours for ethanol and 24 h for deionized (DI)water. Qualitative and quantitative extractables results on sterile connectors using 13 analytical methods showed very low levels of extractables, mostly below the limit of detection (LOD) or no different from the controls. We concluded that the potential for these connectors to release leachable materials into compatible drug products was very low. For the capsule filters, higher levels of extractables were obtained, as expected from the high internal surface area of the microporous membrane within the filter. Qualitative analysis showed that all compounds detected were consistent with the filter's materials of construction, which passed biological safety tests such as USP <88> “Biological Reactivity, in Vivo, for Class VI Plastics.”

Table 1: Single-use components in a test system (Click to enlarge)

In the second study, we characterized extractables from thermoplastic tubing and flexible biocontainers (6). For the tubing, a worst case was represented by presterilizing with gamma irradiation at 50 kGy and agitating the test fluid of ethanol or DI water within clamped segments of tubing for 72 h. Very low levels of extractables were detected, many below the limit of quantification (LOQ). For the biocontainers, a worst case was simulated by filling with test fluid and storing at 40 °C for 30 days. Results showed very few organic compounds above the LOD for water extracts and those identified were in the low parts per million (ppm) or parts per billion (ppb) range. Ethanol extracts gave some additional identifiable compounds, which were mostly oligomers of the base polymers or degradation products of the antioxidants used in the polymer formulations.

Here we report on extractables studies performed on a total system containing all four components previously tested: capsule filter, sterile connectors, plastic tubing, and flexible biocontainers. The test protocol was designed to simulate a typical operating procedure for this type of single-use system and under typical worst-case conditions.