The Usefulness of 0.45 µm–Rated Filter Membranes

Filtration is an important practice in aseptic processing. Microporous membranes are relied upon because of their relatively narrow pore-size distributions. Traditionally, filters with pore-size ratings of 0.2/0.22
m have been considered “sterilizing grade,” meaning that they are expected to produce sterile effluents. Most drug preparations do result in sterility but not all. Therefore, it has been suggested that 0.1
m–rated membranes should be used to remove smaller organisms more thoroughly by sieve retention. A universal substitution of 0.2/0.22
m–rated filters by 0.1
m–rated filters is considered unnecessary, although contexts exist in which filters tighter than a 0.2/0.22
m can be used advantageously. However, one should consider that the smaller the pore-size designation of the filter, the more restricted its flow rate is, and depending upon the degree of particle loading in the fluid, the smaller the throughput that may be obtained.

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