As a former FDA authority, since retired, once observed, “The word ‘absolute’ should be used only in conjunction with vodka.” Absoluteness implies a complete independence from conditions, an inherent ability to retain particles larger that than the filter’s pore size rating, regardless of any other considerations. Without a complete knowledge of the properties of the particles and filter pores at our disposal, the statement is devoid of technical significance or guidance. It may, perhaps, be used in ignorance (although cynics may suspect that its utility derives from marketing efforts, a practice not unknown in the competitive world of sales.)
Control vs. Fear
As Sandman elucidated, human beings like to be in control, and, if this status cannot be achieved, may move rapidly to fear. Unfortunately, when sterile filtration is concerned, fear can result in the installation of wasteful, unnecessary safety nets that can create more problems than they solve.
Being in control is the desired state, and such control can only come from process validation studies. Their authority is at least as old as Lord Kelvin’s basic scientific principle, “When you can measure what you are speaking about, and can express it in numbers, you know something about it.”
It speaks to validation. In sterile filtration, as in most areas of pharmaceutical manufacturing, science-based validation is the best cure for fear.
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