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.