Sterilisation methods filtration

Pharmaceuticals for injection must be presented in a sterile form. Sterility may be achieved by filtration through 0.22 pm filters under aseptic conditions, or by steam, dry heat, radiation or gas sterilisation methods, which may be applied to packaged products. Irrespective of the method, the process must be validated and monitored to assure its effectiveness. As discussed in Chapter 2, this is an example of a process that cannot be assured by verification testing because of its destructive nature. 

The time between the start of the preparation of a solution and its sterilisation or filtration through a micro-organism-retaining filter should be minimised. There should be a set maximum permissible time for each product that takes into account its composition and the prescribed method of storage. 

Sterilisation by filtration differs from the above methods as it removes cells rather than destroys them. It also removes particles and can be used for clarification, carrying out both functions simultaneously. Filtration can be used for both heat sensitive liquids and air supplies to aseptic areas. 

Components of parenteral solutions (active substances, excipients, intermediates and packaging material) should be routinely tested for bioburden and bacterial endotoxin level to ensure they are not adding an excessive microbial load. Bioburden is usually determined on the unfiltered bulk solution. Testing of filtered bulk parenteral solution either before or after filling into the final container may be done by comparison to the previously tested unfiltered bulk solution. Initial bioburden and endotoxin monitoring should be conducted to establish appropriately designed and sized terminal sterilisation methods such as filtration/aseptic filling or terminal heat treatment (see Sects. 30.5 and 30.6). Bioburden is also used as a parameter to evaluate process control. 

Classical sterilisation techniques using an autoclave and saturated steam under pressure, hot water or dry heat are practical and reliable. Other reliable sterilisation methods include membrane filtration, ionising radiatirm sterilisation (gamma and electron-beam radiation) and gas sterilisation (ethylene oxide, formaldehyde). Sterilisation equipment (autoclaves, membrane filters, and other sterilisers) is often used in industrial manufacturing, in preparation in pharmacies, and in other healthcare establishments. Standard sterilisation processes are described in the Ph. Eur., in other current Pharmacopoeias, in ISO standards and National guidelines. 

Final filtration through a sterile 0.2 pm membrane filter is not oifly a sterilisation method, but also an effective way to reduce the initial level of contamination. A pre-filtration (often in-line) with a coarser pre-filter (for example 1.2 pm) is necessary to reduce coarser foreign particles and contamination and to prevent early clogging of the 0.2 pm membrane filter. 

The sterilisation methods (methods of preparation of sterile products) described in the Ph. Eur. are terminal sterilisation methods and filtration [1]. See for filtration Sect. 30.6. In this section an overview of terminal sterilisation methods is given. 

Membrane filtration is the usual alternative sterilisation method in those cases. However membrane filtration as a sterilisation method is less effective and needs aseptic circumstances. If the product withstands a heat treatment at lower steam temperature (100 °C) for 30 min and no pressure, this treatment contributes to the effectiveness and safety of the membrane filtration process. If the solution contains a preservative, as is often the case with eye drops, the effectiveness of the 100 °C treatment may increase considerably. Heat treatment at 100 °C for 30 min over boiling water as such (without additional measures) is not a reliable sterilisation method and hence not recommended by the Ph. Eur. 

For non-aqueous liquids, semisolids and dry powders 2 h sterilisation at 160 °C in dry heat is preferred. Where it is not possible to carry out terminal sterilisation by heat due to formulation instability, a decision should be taken to utilise an alternative method of terminal sterilisation, filtration and/or aseptic processing. It is recognised that new terminal sterilisation processes other than those described in the pharmacopoeia may be developed to provide sterility assurance levels equivalent to present official methods and such processes, when properly validated, may offer alternative approaches. If necessary, a different time-temperature combination may be applied to obtain an SAL of 10 . If too much degradation occurs in dry heat, ionising radiation or gas sterilisation can be applied. If these methods are not suitable either, sterilising membrane filtration and validated aseptic processing, sometimes robotised or with barrier system technology are considered as a last resort. 

Formation of Water—Purification—Storage—Removal of Iron and Algie — Filtration—Hardness—Softening of Hard Waters—Pennutit—Sterilisation of Water—Physical and Chemical Methods... 

Process development studies showed that terminal sterilisation of the gel was not possible. Heat sterilisation and gamma irradiation methods both caused unacceptable physical degradation of the gel and also caused chlorbutol hydrolysis. Aseptic filtration was not possible because the drug was suspended in the gel vehicle and viscosity would also have been a problem. The process described below was therefore developed with consideration of the sterilisation of the product components and the maintenance of asepsis throughout manufacture. 

Due to the potential additional risks of the filtration method as compared with other sterilisation processes, a second filtration via a further sterilised micro-organism-retaining filter, immediately prior to filling, may be advisable. The final sterile filtration should be carried out as close as possible to the filling point... 

Sterilisation can be affected by moist or dry heat, by ethylene oxide (or other suitable gaseous sterilising agent), by filtration with subsequent aseptic filling into sterile final containers, or by irradiation with ionising radiations (but not with ultraviolet radiation). Each method has its particular applications and limitations. Where possible and practicable, heat sterilisation is the method of choice. 

Eye drops are prepared using materials and methods designed to ensure sterility and to avoid the introduction of contaminants and the growth of micro-organisms as also stated by the various Pharmacopoeias. The preparation method consists of several steps dissolution of the ingredients, (sterile) filtration, filling and packaging and (when possible) heat sterilisation. 

For irrigatiOTis steam sterilisation in its final container for 15 min at 121 °C (see Sect. 30.5.1) is preferred. These are the same requirements as for parenteral solutions. An aseptic preparation method with bacterial filtration through a 0.2 pm filter, followed by heating at 100 C for 30 min (or another proper combination of temperature and time or validated aseptic conditimis) is an alternative when one of the substances is sensitive to a higher temperature. If an active substance is not heat resistant at all, only an aseptic preparation with bacterial filtration over a 0.2 pm filter is possible. In such cases the starting materials should be sterile or have a low bioburden and the irrigation should be prepared asep-tically. See also Sect. 30.6. 

Because products that require sterilisation are often aqueous solutions, the initial microbiological contamination can easily be determined in the quality control laboratory by the membrane filtration method (see Sect. 19.6.3). 

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