In most cases, a single filter sufficiently ensures the sterility of a final product. For fluids containing particles, a cascade of prefilters and final filters increases filtration capability. Redundant filtration using two sterilizing-grade filters sequentially is often believed to prevent the loss of a product batch if one filter fails an integrity test. However, this approach increases safety at the expense of filtration performance, which is lowered due to loss of pressure across the first filter.
Aside from the direct cost implications of using multiple filters, there are further considerations around the impact of extractables, adsorption, and integrity testing complexity. However, concerns over increasing costs and other factors should not detract from the economic and safety benefits that can result from more intensive filter usage. A risk-based approach with support from filter suppliers may help the filter user arrive at the appropriate filtration schematic, with the appropriate balance of safety and economy.