To know which sterilization method to choose, it depends on your bioburden, desired SAL and the dose your product can handle. The number of test samples will greatly impact your decision. Since products are required to undergo a sterilization audit every three (3) months, you may want to choose a method that requires less samples to cut down on scrapping product and testing costs.
If your product can withstand at least 15 kGy, VDmax method is your best bet since it requires the lowest number of samples. Dosing at this range is also the most cost effective when sourcing sterilization vendors. Here are some suggestions for samples sizes.
- VDmax15-35 (≈ 46 samples total)
- Typical for a bioburden of 1.5 CFU or higher. Options are for 15-35 kGy in increments of 2.5 kGy. Refer to AAMI TIR33:2005, another guidance document that has tables for additional VDmax testing other than 15 and 25 kGy, shown in ISO 11137-2.
- Method 1 (≈ 120 samples total)
- Used if you’re trying to achieve a low sterilization dose (≤15 kGy).
- B/F = 6 samples
- Bioburden = 10 samples
- Sterilization Validation = 100 samples sterilized at verification dose.
- Used to achieve a SAL lower than 10-6 (i.e., 10-5, 10-4, 10-3, etc.)
- B/F = 6 samples
- Bioburden = 10 samples
- Sterilization Validation = 30 samples (10 samples from 3 lots) sterilized at verification dose.
- Used if you’re trying to achieve a low sterilization dose (≤15 kGy).
- Method 2a or b (≈ 540 samples)
- Used for product with very low sterilization dose and a low bioburden during initial processing.
- Used to determine lowest dose possible and is ideal for radiation-sensitive product.
- Rarest method of testing.
- 9 doses at 60 samples/dose.
- Doses are between 2-18 kGy
- 540 samples tested!
A dose audit consists of the same number of samples minus the B/F samples.
In short, avoid Methods 1 & 2 unless you have a valid justification for using them. Also keep in mind that the tightest tolerance a sterilizer can achieve is ±10%, typically achieved at costly R&D facilities.