Subjects were to assess their symptoms every 15 minutes up to 4 hours after the initial dose or until substantial relief of the defining symptom was achieved. The conservative analysis defined substantial relief as 3 consecutive assessments of improvement of the defining symptom; any attack that did not have 3 consecutive documented reports of improvement was considered a treatment failure. In the less conservative analysis, attacks also were considered to have responded if clinical improvement of the defining symptom occurred but data were incomplete due to cessation of symptom assessments.

A hereditary angioedema (HAE) attack was defined as a discrete episode during which the subject progressed from no angioedema to symptoms of angioedema.

Randomized subjects assessed their symptoms every 15 minutes up to 4 hours after the initial dose of blinded study drug or until substantial relief of the defining symptom was achieved. Substantial relief was defined as 3 consecutive assessments of improvement of the defining symptom. Beginning of substantial relief was considered the first of the 3 consecutive assessments.

An HAE attack was defined as the subject-reported indication of swelling at any location following a report of no swelling on the previous day. Analyses include observed attack counts and normalized attack counts (i.e., the number of attacks observed during each therapy period, normalized for the number of days the subject participated in that period).