The significance of sieve-retention to the filter validation process.

Current efforts at filter validation involve the need to test under "worst case conditions" the bacterial retentive action of filters utilizing the very drug being processed. These concerns recognize that the adsorptive retentions of organisms vary in their efficiencies, depending upon the filtration conditions and the presence or absence of surfactant. The sieve retention of organisms is independent of such conditions, deriving solely from considerations of organism-size, pore-size relationships. Flow-decay studies, can serve to differentiate between filter actions based on sieve-retentions and adsorptive-retentions. A filter's dependence solely upon sieving effects is demonstrable. What is involved is a plotting of flow rates as a function of time in accordance with established mathematical equations. Appropriate plots would indicate the exclusive sieve retention of organisms, a condition of absolute filter reliability deriving from organism-pore size relationships. The clear demonstration by a filter company that its sterilizing filter retains organisms solely by the sieve retention mechanism would suffice to validate that filter for all pharmaceutical filtrations, eliminating the need for individual user validations. The advantage of this mode of filter validation, one based on structurally-inherent filter pore architecture, is that pharmaceutical manufacturers would be free from the need to validate a given filter for each and every pharmaceutical preparation. This would also simplify the FDA's confirmation of filter validation, since a single inspection of the filter manufacturer's records would suffice for all the filter's users.