Channeling effects in the prescription of new therapies: the case of emicizumab for hemophilia A.

To determine if emicizumab was channeled to clinically complex people with hemophilia A upon approval. Claims data (16 November 2017, through 31 December 2019) from US-based insurance databases were analyzed to compare the clinical complexity of people with hemophilia A initiating emicizumab with matched individuals receiving factor VIII (FVIII) episodically or prophylactically. People with hemophilia A with evidence of previous bypassing agent use (indicating FVIII inhibitors) were excluded. Outcomes included bleeding events, arthropathy, pain, comorbidities and healthcare costs. A larger proportion of emicizumab users had bleeding events, comorbidities and arthropathy and greater healthcare costs in the year prior to starting emicizumab compared with FVIII users. Claims-based data limitations prevent an absolute conclusion. Nevertheless, emicizumab users appear more clinically complex than FVIII users, suggesting post-approval channeling.