OBJECTIVES: On-demand or prophylactic factor IX (FIX) replacement therapy is the recommended treatment for hemophilia B patients. Little evidence exists on the effectiveness of FIX in managing bleeding rates when used prophylactically. The aim of this study was to examine real-world evidence on bleeding rates (annualized bleeding rate, ABR) among patients undergoing prophylactic FIX therapy in the U.S.

METHODS: Using IBM MarketScan Commercial Claims and Medicare data from 2010 to 2018 prophylactic FIX therapy initiators were identified. Male patients, with at least 1year of baseline and 1year of follow-up enrollment were included. The analysis focused on prophylactic users defined as having ≥2 FIX prescriptions with no bleeding episodes (hemorrhages, hemarthrosis, effusion, or contusion) in the first 3month after treatment initiation. After a 6month wash-out period, the ABR was estimated using bleeding rates seen in the next 3months (follow up months 10-12). Similar types of bleeding events in similar body parts within 7days were considered as single episodes.

RESULTS: 17,277 FIX claims were identified between 2010-2018 with 1,901 unique patients. Among them, 363 patients met the inclusion criteria and 101 were deemed to be prophylactic users. The mean age in this group was 36.61years. Prophylactic users had an average ABR of 0.36 (nine months after therapy initiation), where the mean number of hemorrhages, hemarthrosis, effusion, and contusion episodes were 0.04, <0.01, 0.12, and 0.20 respectively. On average these patients received 5.80 FIX doses during the entire follow-up year.

CONCLUSIONS: Among prophylactic FIX users, bleeding rates were well controlled. FIX replacement clearly has a protective effect in managing bleeding rates in hemophilia B patients. However, a small sample size and inability to follow-up patients for a longer period are limitations of this study. Future studies should examine long-term effect of FIX therapy on ABR in hemophilia B patients.