Factors affecting tailing in ethylene oxide sterilization part 1: When tailing is an artifact... and scientific deficiencies in ISO 11135 and EN 550.

Current approaches for validation of EtO sterilization cycles identified in ISO 11135 and EN 550 are scientifically deficient and result in full cycle times that are too short. This review article identifies the scientific flaws promulgated in the standards that lead to overestimation of process lethality. The reasons for these deficiencies are design-of-experiment errors that either fail to mathematically account for lag factors or that treat dissimilar samples as a single statistical sample set. Industry's movement toward parametric release, based on erroneous assumptions where exposure time rather than equivalent time is used, may create serious problems. The authors discuss these errors in detail, as well as reasonable methods for correcting them based on formulae for integrated lethality. Application of these methods will allow more accurate calculations of process lethality that are supported by biological data and appropriate mathematical analyses.