While there are different challenge tests protocols, similar methods are described in the EU Pharmacopeia and US Pharmacopeia. These protocols differ one from the other in the detailed procedures, test organisms, criteria for passing the test and the requirements for validation.
Concerning microbiological susceptibility there are difference between three product categories:
- Low microbiological risk products (e.g., products with alcohol content >20%, products based on organic solvents, high/low pH products), for which neither a preservation challenge test nor microbiological quality tests in the finished product are necessary. Nevertheless, scientific justification should be provided detailing the reason why the product is low microbiological risk.
- Single use products, and products which cannot be opened, for which only microbiological quality tests in the finished product are necessary;
- All other products, for which both a preservation challenge test and microbiological quality need to be performed