Sterile filtration

Definition

Sterile filtration is a process in which a liquid containing potentially harmful microorganisms (bacteria, fungi, and some viruses) is passed through a special filter that physically traps microorganisms, removing them from the solution. The filters used for sterile filtration have pores approximately 0.22 micrometers in diameter, which is smaller than the smallest bacteria (approximately 0.5 micrometers). When a microbial-containing liquid passes through the filter under pressure, microorganisms are trapped on the filter surface or within the filter material, while the filtered liquid passes through, now free of microorganisms. Sterile filtration is essential for preparing injectable pharmaceutical preparations, including therapeutic peptides. For solutions that must be sterile but would be damaged by heat sterilization, sterile filtration is the preferred sterilization method. After sterile filtration, the solution must be collected into sterile containers and handled aseptically (using sterile technique) to maintain sterility. Sterile filtration does not remove endotoxins (which are smaller than bacteria), so solutions that require endotoxin removal must undergo additional purification steps.

Sterile filtration is conducted using validated aseptic technique: the filtering apparatus is sterilized (usually by steam sterilization or by being pre-sterilized by the manufacturer), the liquid to be filtered is introduced using sterile technique, and the filtered solution is collected into sterile containers. The filters themselves are certified sterile and are used only once (disposable filters are standard to prevent contamination). Filtered solutions are assumed to be sterile only if the entire filtration process from starting material to final container maintains aseptic conditions.

For research applications, sterile filtration of reconstituted peptide solutions is important for maintaining sterility if the solutions will be used for injection. Researchers must follow aseptic technique carefully during reconstitution and must use sterile, pre-sterilized filtration equipment. The filtered solution should be stored under conditions that maintain sterility (typically at -20°C or lower) in sealed, sterile containers. Documentation of sterile filtration and storage conditions is important for regulatory compliance and for demonstrating that research results are not confounded by microbial contamination.