Measuring the potency labelling of onabotulinumtoxinA (Botox^®) and incobotulinumtoxinA (Xeomin^®) in an LD50 assay

The biological potency of botulinum toxin (BT) drugs is determined by a standardised LD50 assay. However, the potency labelling varies vary amongst different BT drugs. One reason for this may be differences in the LD50 assays applied. When five unexpired batches of onabotulinumtoxinA (Botox^®) and incobotulinumtoxinA (Xeomin^®) are compared in the Xeomin^® batch release assay, the potency variability of both BT drugs fell within the range allowed by the European Pharmacopoiea. Statistical analyses failed to detect differences in the potency labelling of both products. Although the existence of a conversion ratio has been questioned recently, our experimental data are in line with previous clinical experience showing that Botox^® and Xeomin^® can be compared using a 1:1 conversion ratio. Identical potency labelling allows easy exchange of both BT drugs in a therapeutic setting, and direct comparison of efficacy, adverse effects and costs.