Calculation of Spore Log reduction (SLR) from VHP (vaporized hydrogen peroxide) qualification in a pharmaceutical aseptic processing isolator
The formula to calculate Spore Log Reduction (SLR) from VHP (vaporized hydrogen peroxide) qualification in a pharmaceutical aseptic processing isolator is:
SLR = Log10 (N0/Nt)
Where:
N0 = The initial number of spores of the test organism (e.g. Bacillus subtilis) used in the biological indicator.
Nt = The number of fragments of the test organism that remain after exposure to the VHP sterilization process.
The Spore Log Reduction (SLR) is a measure of the effectiveness of the VHP sterilization process in reducing the bioburden. A higher SLR value indicates a higher level of sterilization, as it means that there has been a greater reduction in the number of viable organisms in the environment or equipment.
For example, if the initial number of spores of the test organism is 10^6 (N0 = 10^6), and after exposure to the VHP sterilization process, the number of fragments that remain is 10^3 (Nt = 10^3), the SLR would be:
SLR = Log10 (10^6 / 10^3) = Log10 (10^3) = 3
This result indicates that the VHP sterilization process has reduced the bioburden by 3 log orders, which is a significant reduction.
It’s important to note that the SLR calculation is just one aspect of the validation of the VHP sterilization process. The results from the SLR calculation must be combined with other data, such as temperature and humidity readings, to provide a comprehensive evaluation of the effectiveness of the sterilization process.