Background: The Phase 3 REsearch Evaluating Migraine Prophylaxis Therapy (PREEMPT) trials demonstrated efficacy/tolerability of onabotulinumtoxinA for headache prevention in adults with chronic migraine. This post hoc analysis assessed time of onset of onabotulinumtoxinA after the first treatment in total and responder populations and consistency weekly through five treatment cycles.

Methods: In the 24-week, double-blind, placebo-controlled phase of PREEMPT, individuals were randomized 1:1 to onabotulinumtoxinA (155-195 U) or placebo every 12 weeks for two cycles. The primary pooled efficacy variable was change in headache days per 28 days at week 24. We assessed change in headache and migraine/probable migraine (hereafter migraine) days/week compared with baseline week 4.

Results: Baseline mean (SD) headache days/week (week 4 of baseline) for onabotulinumtoxinA (n = 688) and placebo (n = 696) were similar (4.8 [1.6] vs. 4.8 [1.6] days/week, respectively), as were migraine days/week (4.6 [1.7] vs. 4.6 [1.7] days/week). The effect of onabotulinumtoxinA on change in headache and migraine days/week was significantly greater than placebo at week 1, persisting from week 3 after the first treatment (−1.6 [2.2] vs. −1.1 [2.2] headache days/week [ p < 0.001] and −1.6 [2.2] vs. −1.1 [2.2] migraine days/week [ p < 0.001]). Headache and migraine days decreased in onabotulinumtoxinA responders beginning 1 week after treatment 1.

Conclusions: Treatment with onabotulinumtoxinA is associated with significant reductions in headache and migraine days/week at week 1, persisting after week 3, compared with placebo. Combined with earlier reports showing onabotulinumtoxinA treatment results in a persistent and progressive reduction in headache days over 56 weeks, it is suggested peak benefit may require multiple treatments.