MELBOURNE – Longer follow-up data from the four HAVEN studies of emicizumab in patients with hemophilia A has shown further reductions in bleeding rates without any significant safety concerns, according to data presented at the International Society on Thrombosis and Haemostasis congress.

Michael Callaghan, MD, of the Children’s Hospital of Michigan, Detroit, reported on a pooled analysis of data from 399 patients with hemophilia A who were treated with emicizumab (Hemlibra) for a median duration of 83.1 weeks, representing 650 patient-years of exposure. The studies included pediatric and adult patients, both with and without factor VIII inhibitors.

Patients enrolled in the studies had a median of eight bleeds in the 24 weeks before enrollment, but in the first 24 weeks of treatment with emicizumab, the mean annualized bleed rate dropped to 1.9. During weeks 25-48, this dropped further to 0.8, remained at that level in weeks 49-72, then declined further to 0.3 during weeks 73-96.

During the first 24 weeks of treatment, 70.8% of patients experienced zero bleeds, and 22.5% experienced 1-3 bleeds. By week 96, the number of patients experiencing zero bleeds had increased to 88.6% and nearly 100% of patients had had fewer than three bleeds during that 24-week period.

The study also reported on target joint bleeds and showed the mean annualized bleed rate in target joints decreased from 1.4 in the first 24 weeks of treatment to 0.3 in weeks 73-96, by which time 90.4% of patients reported no target joint bleeds at all. Overall, 99.2% of target joints resolved, which was defined as two or fewer spontaneous bleeding events into a target joint in a year.

“The bleed rate seemed to converge on a low number, suggesting that maybe patients that came with preexisting synovitis or inflamed joints improved over time to resemble the patients who had better joint health at the beginning of the study,” Dr. Callaghan said.

The long-term follow-up did not reveal any major safety concerns. The most common drug-related adverse event was injection site reactions, which just over one-quarter of patients reported. The main serious adverse events were bleeding related.

“With any biologic agent, we were concerned about antidrug antibodies,” Dr. Callaghan told the conference. “At this follow-up point, less than 1% of patients treated with emicizumab in this group have had neutralizing antidrug antibodies.” Most of these antibodies were detected with routine screening, but there was one patient with antidrug antibodies who developed breakthrough bleeding during the study.

In an interview, Dr. Callaghan said emicizumab was “game-changing” therapy, and that the data showed it was efficacious even long term. However, he said there were still some questions to be answered about which patients were most likely to benefit.

“How early do we start this? Do we put previously untreated patients on this, and if we do, how do we expose them to factor VIII?” he said. Other challenging questions are whether to do immune tolerance induction for patients with factor VIII inhibitors and how the drug would work for other patient groups, such as those with comorbidities or who were very active.

The study was sponsored by F. Hoffman-La Roche and Chugai Pharmaceutical. Dr. Callaghan declared consultancies, grants, clinical trial involvement, speakers bureau engagements, and shares with the pharmaceutical sector.

SOURCE: Callaghan M et al. 2019 ISTH Congress, Abstract OC 60.2.

Emicizumab follow-up shows further bleeding declines