A randomized, double-masked, crossover comparison of the efficacy and safety of botulinum toxin type A produced from the original bulk toxin source and current bulk toxin source for the treatment of cervical dystonia.

In 1997, the US FDA approved a new bulk toxin source (now referred to as current) for the manufacture of botulinum toxin type A (BTX-A). The current BTX-A preparation has a lower neurotoxin complex protein load than the original BTX-A preparation, which may reduce antigenic potential. The present double-masked, multicenter study compared the efficacy and safety of BTX-A (BOTOX) produced from both original and current bulk toxin sources for the treatment of cervical dystonia.