Study to Evaluate the Efficacy and Safety of Erenumab (AMG 334) in Migraine Prevention

A migraine day was any calendar day in which the participant experienced a qualified migraine headache (onset, continuation, or recurrence of the migraine headache). A qualified migraine headache was defined either as a migraine with or without aura.

The change from baseline in monthly migraine days was calculated as the average number of migraine days per month during the last 3 months (months 4, 5, and 6) of the 24-week double-blind treatment phase - the number of migraine days during the 4-week baseline phase.

A migraine day was any calendar day in which the participant experienced a qualified migraine headache (onset, continuation, or recurrence of the migraine headache). A qualified migraine headache was defined either as a migraine without aura or a migraine with aura.

At least a 50% reduction from baseline in monthly migraine days was determined if the change in monthly migraine days from the 4-week baseline phase to the last 3 months (mean of months 4, 5 and 6) of the 24-week double-blind treatment phase * 100 / baseline monthly migraine days was less than or equal to -50%.

Monthly acute migraine-specific medication treatment days is the number of days on which migraine specific medications were used between monthly doses of study drug. Migraine-specific medications includes two categories of medications: triptan-based migraine medications and ergotamine-based migraine medications.

The change from baseline in monthly acute migraine-specific treatment days was calculated as the average number of migraine-specific treatment days per month during the last 3 months of the 24-week double-blind treatment phase - the number of migraine-specific treatment days during the 4-week baseline phase.

The Migraine Physical Function Impact Diary (MPFID) is a self-administered 13-item instrument measuring physical functioning. It has two domains, Impact on Everyday Activities (7 items) and Physical Impairment (5 items), and one stand-alone global question. Participants completed the MPFID daily in an electronic diary based on the past 24 hours. Participants responded to each item on a 5-point scale, with difficulty items ranging from "Without any difficulty" (1) to "Unable to do" (5) and frequency items ranging from "None of the time" (1) to "All of the time" (5). For each domain, the scores were calculated as the sum of the responses and rescaled to 0 - 100, with higher scores representing greater impact of migraine.

Change from baseline was calculated as (mean monthly average physical impairment scores as measured by the MPFID over the last 3 months of the double-blind treatment period) - (baseline monthly average physical impairment scores as measured by the MPFID).

The Migraine Physical Function Impact Diary (MPFID) is a self-administered 13-item instrument measuring physical functioning. It has two domains, Impact on Everyday Activities (7 items) and Physical Impairment (5 items), and one stand-alone global question. Participants completed the MPFID daily in an electronic diary based on the past 24 hours. Participants responded to each item on a 5-point scale, with difficulty items ranging from "Without any difficulty" (1) to "Unable to do" (5) and frequency items ranging from "None of the time" (1) to "All of the time" (5). For each domain, the scores were calculated as the sum of the responses and rescaled to 0 - 100, with higher scores representing greater impact of migraine.

Change from baseline was calculated as (mean monthly impact on everyday activities scores as measured by the MPFID over the last 3 months of the double-blind treatment period) - (baseline monthly impact on everyday activities scores as measured by the MPFID).