Intraindividual bleeding outcomes in haemophilia A patients on emicizumab prophylaxis in Australia

Aim: Emicizumab became routinely available in Australia in November 2020 as regular prophylaxis for certain haemophilia A (HA) patients. We performed an intraindividual comparison of bleeding outcomes in Australian HA patients before and after commencement of emicizumab. Method: Data were extracted from the Australian Bleeding Disorders Registry (ABDR) on HA patients using emicizumab regarding demographics, severity, treatment, inhibitors and number and type of intraindividual treated bleeds before and after starting emicizumab. Results: As of April 2022, there were 459 eligible HA patients on emicizumab in Australia, 86% (397/459) of which had severe disease. 13% (59/459) had a current inhibitor. Adults (>18 years) composed 49% (223/459) of the population. The proportion of patients with zero bleeds increased from 54% to 63% after commencement of emicizumab [relative risk (RR) 1.24, 95% confidence interval (CI) 1.09-1.41, p<0.01]. RR for zero treated bleeds post-commencement was significant in subgroups including paediatric patients (RR 1.34, 95% CI 1.13-1.59, p<0.01) and those not on regular prophylaxis prior (RR 1.75, 95% CI 1.22-2.52). There was no significant difference in zero-bleed prevalence in the adult, standard half-life (SHL) and extended half-life (EHL) subgroups. Spontaneous bleeding reduced (RR 1.69, 95% CI 1.34-2.13, p<0.01), while provoked bleeding did not (p=0.15). Conclusion: Real-world data from Australia shows a reduction in bleeding events with emicizumab prophylaxis for the overall population of HA patients, though not in all subgroups. This reduction appears to be most pronounced in spontaneous bleeds within the paediatric population, and in those on on-demand therapy prior to switching.