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Pharma Newsletters >> Eurofins BioPharma Services Newsletter 20 - June 2018 >> Antibiotic assay validation

Eurofins BPT Toronto offers USP<81> antibiotic assay validation & routine testing capabilities

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By Michelle Taube, Business Development Manager, Eurofins BioPharma Product Testing Toronto Inc. 

The USP chapter covers microbial assays for determining antibiotic activity (potency). The effectiveness of antibiotics can be determined by their ability to inhibit the growth of microorganisms under appropriate conditions. Experchem Laboratories Inc. joined the Eurofins family in June 2015 and has been rebranded as Eurofins BioPharma Product Testing Toronto. This acquisition has brought the capacity to test USP for antibiotic products into the Eurofins BPT North American laboratory network.

USP covers 29 antibiotics. Bacitracin, Gramicidin, Neomycin and Polymyxin B are the most common antibiotics used in OTC consumer products. There are two general techniques used to determine antibiotic activity. The cylinder plate method assay measures the dispersion of the antibiotic from a vertical cylinder through a solid agar petri plate. The growth of the specified microorganism is prevented in a circular zone surrounding the cylinder which contains the antibiotic solution. The second technique is called turbidimetric assay which involves mixing a solution of the antibiotic in a liquid media that is favourable for the specified microorganism growth in the absence of an antibiotic. Antibiotic potency is characterised by microbial growth inhibition and is calculated based on triplicate assays at different concentrations.

To use the general method outlined in USP a method validation must be performed for use on a finished product. During the validation, a maximum value for the confidence interval width is established, which is used in the calculation to estimate antibiotic potency. Any product containing one or more of the 29 antibiotics will require antibiotic assay to confirm potency using the USP chapter. Common product matrices tested at Eurofins BPT Toronto include antibiotic ointments, creams, ophthalmic solutions, and feed additives. Eurofins BPT Toronto can explore other product matrices and help develop appropriate extraction protocols as needed.

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