A comparison of the spread of three formulations of botulinum neurotoxin A as determined by effects on muscle function.

The purpose of these experiments was to compare the spread of three formulations of botulinum neurotoxin A. A gelatin/phosphate buffer (C), DysportR (D {0.5 U}, BotoxR (B {0.167 U}), or a purified preparation of botulinum neurotoxin A [Bont A] (BA {0.5 U}) was injected into the tibialis anterior of male, Wistar rats. After 4 days, the adjacent extensor digitorum longus muscle was isolated in situ and the nerve was maximally stimulated to determine contractile properties and the rate of fatigue. There were no differences in body or muscle weights between any of the groups after 4 days of treatment. Maximal twitch and tetanic tensions were decreased reverse similar 25% (p < 0.05) in all treatment groups compared to C. In addition, rate of tension development was significantly less in all treatment groups compared to C but one-half relaxation time and time to peak tension were not different between any groups. Fatigue of the muscle was significantly faster in all groups compared to C but there was no difference between treatment groups. These data indicated that botulinum toxin A injected intramuscularly was likely to spread to adjacent muscles but that the spread was not different between the three formulations tested. The effect of the spread ranged from a slight to a severe reduction in maximal tension but this did not occur in all animals studied. Copyright Rapid Science Ltd