Sterilisation methods ionising radiation

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. 

Sterilisation by means of ionising radiation of pharmaceutical preparations is not allowed in a number of countries. Many active substances and raw materials are decomposed by the doses required for sterilisation. Some polymers become brittle and glass may become discoloured. For these reasons there is only limited application for this sterilisation method for pharmaceutical preparations. Radiation sterilisation is however widely used in the medical device industry. 

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. 

Ionising radiation sterilisation an absorbed radiation dose of at least 25 kGy. This method leads to breaks in the DNA of micro-organisms and, in presence of water, the formation of free radicals. 

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. 

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