The term sterility refers to the absence of viable any microorganism; bacteria, spores, and viruses in a product. Viable microorganisms proliferate in the product eventually destroying it and making it unsafe for use. It is therefore important to have sterility validated. Pharmaceutical manufacturers have to ensure sterility of their products especially those intended for parenteral or implant sterilization use. Assurance of sterility, therefore, guarantees that these products are of quality, efficacious and safe to use. Sterility Assurance Level (SAL) is a ratio that enables the Sterile Pharmaceutical Manufacturers to give an arbitrary number to show the level of sterility in their product.
Sterility Assurance Level Concept
As mentioned above, SAL is a ratio. It gives the probability of having a viable microorganism in a product. For instance, the standard accepted sterility assurance level is 10-6. This means that for every one million products that have undergone the sterilization process there is at least no more than one viable microorganism. However, there are different SAL depending on the intended final use of the product and the stability of the product to the sterilization. For example
• Standard level assurance 10-6 also referred to as pharmaceutical sterilization is intended for parenteral pharmaceutical products that are heat-resistant
• Standard level assurance 10-4 (SLA 10-4) referred to as high-level sterilization intended for heat resistant medical devices
• Standard level assurance 10-3 (SLA 10-3) referred to as low-level sterilization is intended for reusable medical devices that have a validated after use cleaning process.
Sterile Pharmaceutical Manufactures, however, face the problem of evaluating the success of the sterilization process employed. A Standard Level Assurance of 10-6 is all but impossible to record in an experiment. Therefore, to overcome this limitation sterility assurance level of a sterilization is got from model experiments. Conclusions, drawn from these experiments, ascertain a given standard level assurance.
In this case, Sterility Assurance Level can be used to define the number of microbes that are destroyed under given sterilization conditions. In this case, a pre-determined number of microorganism is subjected to a sterilization process. Then the number of microorganisms after the test are then determined. The bio indicators are contaminated with the maximum resistant microorganism to the given sterilization process. This enables to encompass all probable microorganisms susceptible to the sterilization.
For example, a sterilization process that results to the destruction of 106 of the resistant microorganism in the bio-indicator can guarantee a standard level assurance of 10-6. Usually the “Half Cycle Method” is used. It involves subjecting the resistant microorganism in the bio-indicators to half the conditions expected in the actual sterilization process. Most often the resistant organism is subjected to half the time, but all the conditions of the other sterilization procedures are not changed. Therefore, to ascertain the success of the actual sterilization process, the “Half Cycle Method” must achieve a corresponding sterility assurance level. This means that if the “Half Cycle Method” sterilization process achieves a standard assurance level of 106 it will guarantee a sterility assurance level of 10-6 when applied to the final product. The “Half Cycle Method” test ensures that the final product is subjected to “overkill” conditions.