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Vacuum H2O2 gas sterilisation in lyophilisers: a future alternative?
Lyophiliser sterilisation is a common demand of the pharmaceutical industry. This is done by steam by nearly 100% of all applications on the market. During this process, pressurised, saturated, clean steam at temperatures >121.1 °C for 1530 min is applied to the system. However, an alternative to steam sterilisation could be H2O2 (hydrogen peroxide) gas sterilisation, which is operated under vacuum conditions.
First, the area to be sterilised (chamber, condenser, all associated pipes) is evacuated to a certain value (approximately 0.02 mbar) and then H2O2 gas is transferred into the evacuated area. Because of the high vacuum, only a small amount of H2O2 gas is required to cover the entire surface area, including difficult‑to‑reach parts (as an estimate, the design calculation uses 10 mL/m3, which will be reduced to real requirements during cycle development). The final pressure during sterilisation will be approximately 10 mbar. This approach can be repeated for process safety reasons.
This piece compares steam sterilisation with H2O2 gas sterilisation.
Advantages of classical steam sterilisation
In most facilities, sufficient amounts of steam are available and its quality is compliant with the requirements. Lyophilisers often use steam as a media for defrosting (CIP water can also be used). If a steam connection is already in place, it is probably best to sterilise with steam.
Advantages of H2O2 gas sterilisation
Both methods have a sterility assurance level (SAL) 10−6. High vacuum in the entire system ensures all dead legs will be sterile (ISO 13408‑4‑compliant) and, unlike steam sterilisation processes, there is no risk of remaining water condensate.
Because of the gentle H2O2 gas sterilisation process at ambient temperature, stress to the vessels, diaphragms, joints and filter is reduced. In addition, the low concentration of H2O2 gas applies no stress to non‑stainless steel components. The ambient temperatures mean less insulation material and related insulation work are required.
There is no process‑related overpressure in the system and, therefore, no pressure vessel is required, which avoids costs for pressure vessel calculation, approval and periodic inspection. The absence of high pressure and high temperatures avoids unexpected events, such as leaks, and raises the production availability.
Existing steam pipework systems within the facilities are often limited because of capacity. This requires interlocks with other steam consuming systems to avoid potential lack of steam. The risk of rouging out (i.e., dark iron deposits), which can be associated with steam supply, can be eliminated.
Comparable aspects for both methods
The purpose of validation is to verify that the SIP system design, process design, design of all facilities, equipment and materials used meet requirements for the intended use. Both methods require validation and the same acceptance criteria (SAL 10−6). Therefore, the test approach and the amount of related testing is comparable. The main difference is the determination of critical areas. Steam SIP uses temperature mapping to verify that all potential cold spots reach the required temperature of >121.1 °C.
H2O2 gas uses temperature mapping to identify the warmest positions within the system after the previous CIP cycle.
H2O2 gas performs best within the 1550 °C temperature range. Mapping, therefore, supports process development while defining worst case position, which will later be biological indicator (BI) tested.
The use of H2O2 gas sterilisation will be more often used as a retrofit in existing lyophilisers. In the near future, this method will have niche application for new equipment; for example, facilities where insufficient amounts of clean steam is available. However, if we assume energy costs will continue to rise and more environmental directives will come into play, H2O2 gas sterilisation could offer a serious alternative to steam sterilisation.
Based on a contribution by Mike Guttzeit, Team Leader, Validation, from GEA Pharma Systems (Germany).