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INTRODUCTION: Extended half-life factor IX concentrates (EHL-FIX) can be administered weekly to prevent bleeding for persons with severe haemophilia B. We report the experience of a large UK haemophilia comprehensive care centre using low dose EHL-FIX for persons with severe haemophilia B. AIM: The low doses used in real world are approximately half of the doses used in clinical trials. We aim to assess the efficacy and safety of low dose EHL-FIX. METHODS: Data from a cohort of 13 patients who were switched from standard half-life factor IX (SHL-FIX) to Alprolix® (mean dose 31.5 IU/kg) and seven patients who switched from standard half-life factor IX to Idelvion® (mean dose 20.2 IU/kg) were included. RESULTS: The median annualized bleeding rate was similar for SHL-FIX (median 3, interquartile range [IQR] 1-5) and EHL-FIX (median 3, IQR 1-5.25). Quality of life scores, measured using the European Quality of Life 5 Dimensions assessment were similar for SHL-FIX (median 0.76, IQR: 0.63-0.84) and EHL-FIX (median 0.79, IQR: 0.58-0.88). CONCLUSION: This study shows that EHL-FIX given at low doses can be effective for prevention of bleeding for persons with severe haemophilia B.

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annual bleeding rate, bleeding disorders, extended half-life factors, factor IX, haemophilia