A Study to Evaluate Botulinum Toxin Type A for Injection（HengLi®）for Prophylactic Treatment of Chronic Migraine

Subjects in the core phase will be randomized into two groups: Botulinum Toxin Type A (HengLi®) (155U to 195U) or placebo. Study include a 28-day baseline screening period, a 24-week core phase with 2 administrations, and a 32-week extension phase with 3 administrations .Subjects enrolled will get a e-headache-diary in recording their headache symptoms and acute headache medications. HengLi® was administered as 31 fixed-site, fixed-dose (5U), i.m. injections across 7 specific head/neck muscle areas every 12 weeks (weeks 0, 12, 24, 36, and 48). At the investigator's discretion, up to 40 U of additional HengLi® could have been administered among 3 muscle groups (occipitalis, temporalis, or trapezius) using a protocol-defined paradigm. Hence the maximum dose per treatment cycle was 195 U over 39 sites. Efficacy Outcome Measures should be evaluated by headache diary, HIT-6 score and MIDAS score . The primary Outcome Measure: Change from baseline in the average number of days with headache per month (The last 4 weeks during the core phase and the 4 weeks during the baseline period should be compared with the number of headache days per month on average.)