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The main focus of the letter to the editor by Dr Pickett[1] is the interchangeability of botulinum toxin A dosages between products, and therefore this answer will address this issue.
In contrast to the argument of Dr Pickett, it is justified to draw conclusions on botulinum toxin A products based on the potency. It is true that the units of each product are determined by different LD50 (median dose that is lethal to 50% of animals tested) assays. However, it had been shown that the potency assay carried out by Merz resulted in the same number of units for Botox®/Vistabel® as for Xeomin®/Bocouture®. More importantly, it was demonstrated in several clinical studies for neurologic indication[2,3] as well as in the aesthetic field[4,5] that Botox®/Vistabel® and Xeomin®/Bocouture® are equipotent. This fact is acknowledged in the summary of product characteristics of Bocouture®.[6] It is therefore justified to calculate a specific neurotoxin potency based on the potency in each vial, clearly demonstrating that Xeomin®/Bocouture® requires the lowest amount of clostridial protein to achieve the same therapeutic effect. The reported reduced value for the protein content in the Xeomin®/Bocouture® vial has been explained in the article[7] and is attributed to the increased sensitivity and precision of the ELISA method used compared with older methods used in the past.
References
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Acknowledgements
Dr Jürgen Frevert is an employee of Merz Pharmaceuticals GmbH, Frankfurt, Germany.
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Frevert, J. Author’s Reply. Drugs R D 11, 98–99 (2011). https://doi.org/10.2165/11591800-000000000-00000
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DOI: https://doi.org/10.2165/11591800-000000000-00000