Long-term efficacy and respective potencies of botulinum toxin A and B: a randomized, double-blind study

Mouse units (mU) are used for quantification of the biological activity of botulinum A and B toxin preparations. However, in human tissue, mU values between preparations are not equivalent and lack of clarity concerning efficacy and safety remains with regard to their respective potencies, duration of drug effect and diffusion qualities.

To compare short-term and long-term effects of Botox(®) (BOT; Allergan Inc., Irvine, CA, U.S.A.) and Neurobloc(®)/Myobloc(®) (NBC; Solstice Neurosciences Inc., Malvern, PA, U.S.A.) in different doses and dilutions in a human skin model.

In this prospective randomized double-blind study, 18 healthy volunteers (eight women and 10 men; mean ± SD age 28·4 ± 5·7 years) were injected intradermally with pure saline, BOT and NBC at 10 points in the abdomen in random order, using the BOT/NBC conversion ratio 1 : 75 and different dilution schemes. For an objective outcome, the ninhydrin sweat test was used to compare the anhidrotic areas (action halos). Ten measurements were taken during a time period of 54 weeks.

Both preparations showed a peak effect at week 3, with significantly larger anhidrotic areas for NBC. Thereafter, however, the rate of decline was lower in BOT and after week 24, mean BOT areas were larger. The effect of dilution was higher in NBC and the mean dose equivalence conversion ratio (BOT/NBC) was 1 : 29 (area under the curve). Gender effects were seen in both products, with smaller action halos in women.

These results have important implications in clinical routine, especially for autonomic indications.