Why disinfectants are filtered through 0.22 µm filters in pharmaceuticals?

Disinfectants are used to control contamination in any area. Filtration of disinfectants depends upon the criticality of the area which we want to clean. For example if disinfectants are used for general area then there in no need to filter the disinfectants because there is no control over the general area and no critical activity performed there. But if disinfectants are used for the aseptic area then these disinfectants must be filtered through 0.22 µm filters. 

Now the questions comes in mind why we need filtration of disinfectants for use in aseptic area and another is disinfectants are used to reduce or kill microorganisms then what is the requirement of filtration?

The answer for these question is that aseptic area is that area where we handle or manufacture sterile products. Any aseptic area is divided in to different classes like A,B,C and D. These classes are defined mainly on the basis of non viable and viable particles. In these different classes we have defined limit of non viable and viable particles and any increase from the specified limit could cause failure of manufacturing area. If we use disinfectants in aseptic area after filtration through 0.22 µm filters then there will not be any chance of increasing the non viable particles in aseptic area which disinfectants could carry during the process of disinfectant preparation otherwise application of disinfectants in aseptic area without filtration can increase non viable particles in area and can cause failure of aseptic area. Another reason is that though disinfectants are used to kill microorganisms but there are some disinfectants which could carry contamination in aseptic area hence require filtration. For example 70% IPA is very effective against bacterial and fungal vegetative cells but there is one limitation of this disinfectant. 70% IPA is not effective against spore cells. Spores cells are very hard to kill and 70% IPA can't kill spores cells. So, it must be filtered through 0.22 µm filters otherwise it may carry spores cell in aseptic area. So, to control non viable particles and viable contamination in form of spores, disinfectants must be filtered through 0.22 µm filters before use in aseptic area.