The safety and efficacy of botulinum toxin type B in the treatment of patients with cervical dystonia: summary of three controlled clinical trials.

Cervical dystonia (CD) is characterized by abnormal, involuntary contractions of the cervical and/or shoulder muscles. Direct injection of Botulinum toxin type A (BTX-A) into the affected muscles has been used successfully to treat this condition. However, clinical resistance to BTX-A therapy develops in a limited number of patients. Moreover, an unknown proportion of treated patients have a suboptimal response to their present therapy. BTX-B is antigenically distinct from BTX-A and possesses a different mechanism of action. Three randomized, double-blind, placebo-controlled clinical trials evaluated the safety and efficacy of BTX-B (Elan's BTX-B evaluated as NeuroBloc) as a treatment for patients with CD. Patients received a single dose of BTX-B ranging from 2,500 to 10,000 U. The primary efficacy evaluation for each of these studies used the Toronto Western Spasmodic Torticollis Rating Scale (TWSTRS) total score. Additional efficacy measures included the TWSTRS severity, disability, and pain subscale scores, as well as the Patient Analog Pain Assessment and Patient's and Physician's Global Assessments of Change. In all three studies, groups receiving BTX-B displayed statistically significant improvements in TWSTRS total score and other efficacy end points compared with those who received placebo treatment. The clinical benefits after BTX-B treatment lasted 12 to 16 weeks and were observed in both BTX-A-responsive and BTX-A-resistant patients. In general, treatment with BTX-B was well tolerated and most of the reported adverse events were of short duration, mild to moderate in severity, and anticipated. The results from the three controlled clinical trials demonstrate the safety and efficacy of BTX-B in the treatment of patients with CD, including those who are resistant to BTX-A treatment.