Botulinum toxin type B (Myobloc) in subjects with hemifacial spasm: results from an open-label, dose-escalation safety study.

Objective: Evaluate the safety of botulinum toxin type B (BoNT-B) in subjects with hemifacial spasm (HFS).

Methods: This open-label, sequential dose-escalation study evaluated BoNT-B in subjects with HFS. Eligible subjects were enrolled and received a single injection of one of four sequential BoNT-B doses (100, 200, 400, or 800 U). Following injection, subjects were evaluated in person at Weeks 2 and 8 and by phone at Weeks 1, 4, and 10 and every 2 weeks thereafter until benefit was lost. Safety was assessed by adverse events (AEs), vital signs and clinical laboratory evaluation. The severity of HFS was assessed using a patient social impairment visual analog scale (VAS), subject severity of contraction VAS, the HFS physician assessment, and subject HFS frequency and severity assessment.

Results: Nineteen predominately Caucasian (92%) and female (67%) subjects (aged 36-80 years) with HFS participated in this study. Subjects remained in the study an average of 88 days (range of 41-332 days) after receiving a single dose of BoNT-B. No deaths, serious AEs or AEs leading to trial discontinuation occurred during the study period. Two subjects in the 400 U dose group requested early withdrawal, whereas all other subjects completed the study. A reduction in HFS severity was observed in subjects treated with doses of 200 U or more. Improvements in subject HFS assessments tended to return to baseline values by 8 weeks following injection.

Conclusion: BoNT-B was well-tolerated and reduced HFS severity in subjects who received injections of 200 to 800 U. Additional investigation is necessary to confirm the findings from this open-label study.