Switch from Intravenous C1-Inhibitor C1-INH(IV) to Subcutaneous C1-Inhibitor [C1 INH(SC)] for Routine Prevention of Hereditary Angioedema (HAE) Attacks: Subgroup Findings from the Compact Trial

The COMPACT (Clinical Studies for Optimal Management of Preventing Angioedema with low-volume subcutaneous C1-Inhibitor Replacement Therapy) trial evaluated the safety and efficacy of a low-volume C1-INH(SC) as routine prevention in patients with HAE. This subgroup analysis was designed to compare HAE attack rates in patients who stopped their prior C1-INH(IV) as routine prophylaxis to start C1-INH(SC) routine prevention during participation in the COMPACT trial. This was a pre-specified subgroup analysis of 22 subjects who used C1-INH(IV) for routine prophylaxis of HAE attacks prior to using C1-INH(SC) during COMPACT trial participation. The time-normalized rate of HAE attacks (number/month) experienced during pre-study C1-INH(IV) prophylaxis was determined for the 3 month period prior to COMPACT trial entry and compared against the time-normalized attack rate during study treatment with C1-INH(SC), 40 or 60 IU/kg. The mean (SD) time-normalized HAE attack rate (number/month) during pre-study use of C1-INH(IV) prophylaxis (n=22) was 2.56 (2.579), compared with 1.73 (2.902) while using C1-INH(SC) for routine prevention in the COMPACT study. Following a switch to C1-INH(SC), the mean (SD) percentage reduction in HAE attack rate compared to prophylactic C1-INH(IV) use was 52.1% (63.64%). The corresponding mean (SD) percentage reductions in HAE attack rates by C1-INH(SC) dose were 48.8% (68.37%) for C1-INH(SC) 40 IU/kg, and 53.7% (64.23%) for C1-INH(SC) 60 IU/kg. This subgroup analysis of COMPACT trial data suggests that patients previously using C1-INH(IV) prophylaxis and switched to C1-INH(SC) (40 or 60 IU/kg) for routine prevention may experience a lower attack rate than experienced during routine prophylaxis with C1-INH(IV).