Microbiological potency testing of antibiotics: facing USP and EP requirements

Luciana lucci, Head Of Micro, Eurofins BioPharma Product Testing, LucianaIucci@eurofins.com

For several antibiotics, the European Pharmacopoeia 2.7.2 and USP specifications about the product potency require testing through microbiological assays. The activity of the antibiotic is estimated by comparing the inhibition of the growth of susceptible strains, produced by different concentrations of the test sample, compared to the one coming from a reference preparation.

The advantages of microbiological methodology (diffusion or turbidimetric methods), as opposed to chemical assays, are represented by the possibility to measure the activity directly on a specific microorganism, taking into account the actual availability of the active substance as well as the ability to determine the activity of a substance without the information of the exact qualitative composition.

The diffusion method is based on the diffusion of the antibiotic in the solid culture media. The test sample and the reference standard are placed on the surface of a solid medium inoculated with a microorganism suspension; the growth of the microorganism into the culture medium will be visibly inhibited after the incubation.

The turbidimetric method is based on the inhibition of the growth of a sensitive microorganism in liquid culture exposed to different concentrations of the antibiotic. The inhibition is measured by the different degree of turbidity of the suspension, which is proportional to the different level of microbial growth.

EP and USP mainly differ on the design of the assay itself and the choice of mathematical models used to determine the potency.

Eurofins is able to support pharmaceutical companies needing to perform GMP testing on antibiotic-based drug substances or drug products in selecting the proper test system based on regulatory requirements and running the actual testing according to either USP or EP test methods.

For more information, visit www.eurofins.com/pharma-services/biopharma-product-testing