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A Clean Bill of Health


A Clean Bill of Health

James Finn describes the development of the IChemE award-winning setup for sterile filtration of APIs for The Chemical Engineer.

When you are dealing with the manufacture of an intravenous pharmaceutical product, sterility is key. A vital stage in ensuring this is the sterile filtration of bulk APIs (active pharmaceutical ingredients) and excipients (prior to their introduction into a sterile process train) to remove bacteria, micro-organisms and particulates which may be harmful to the patient. This is typically achieved using a filter with a nominal pore size of 0.22 µm.

When you are dealing with an antibiotic that is also on the World Health Organization’s List of Essential Medicines, being able to guarantee and prove that sterility, allowing for expeditious release of the final product, is vital to maintaining supply to critically ill patients.

Confirming the integrity of the sterile filters is key to ensuring process sterility. This is usually achieved by taking the filter offline, inserting it into a test rig, wetting the filter with either water or a solvent and then conducting a diffusion, bubble-point or a water intrusion test. These tests pressurise the filter with air, and monitor diffusion through to the downstream side of the filter. The rates of diffusion correlate to different pore sizes, allowing the integrity of the filters to be confirmed. To facilitate the test, the downstream side of the filter needs to have a route open to atmosphere, usually an open vent pipe, or a route back to the non-sterile test rig.

As the filter usually needs to be positioned in an offline rig to perform the integrity test, integrity of the filter is confirmed prior to installing it in the process stream and running the pre-production steam sterilisation step.

As the filter is tested prior to installation and steam sterilisation, the majority of batches are run with the risk that steam sterilisation may have damaged the filter. High pressure drops across the filter, or rapid changes in temperature, can affect the filter cartridge and create routes through the filter which would allow bacteria and micro-organisms through into the final batch. Damage is typically only discovered during the post-batch integrity test, resulting in a lost batch.

Once the production process has been completed, the filter can be taken offline again and re-tested, post use, to confirm that the filter has not been damaged.

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