This is a parallel, Phase 3, two-arm, open-label study to evaluate the efficacy and safety of treatment with fitusiran prophylaxis administered to male pediatric participants (aged 1 to \<12 years) who have severe hemophilia A or B, with or without inhibitory antibodies to FVIII or FIX.
Number of participants:
Approximately 85 participants will be enrolled into the study:
* Approximately 60 fitusiran-naïve participants with severe hemophilia A or B, with or without inhibitors (fitusiran-naïve arm), and * Approximately 25 participants with severe hemophilia A or B with inhibitors rolling over from the EFC15467\* dose confirmation study (roll-over arm).
* Fitusiran has been investigated in the pediatric population in study EFC15467, which enrolled male participants aged 1 to \<12 years with hemophilia A or B with inhibitors to examine the safety and tolerability of fitusiran in the pediatric population.
Participants will be enrolled into 1 of 2 arms:
* Fitusiran-naïve: these participants have not previously received fitusiran, and they will undergo screening and study eligibility assessments. Once enrolled, they will go through a 24-week standard of care (SOC) period before starting fitusiran prophylaxis. * Roll-over participants from the EFC15467 study: only participants who are still on active treatment in study EFC15467 and consenting to study EFC17905 will be eligible to roll over. They will not need to undergo screening or further eligibility assessments. They will directly enroll into the fitusiran treatment period and continue treatment on their current fitusiran dose.
The duration of fitusiran treatment will be up to 160 weeks for the fitusiran-naïve arm and up to 60 weeks for the roll-over arm.
Participant must be 1 to <12 years of age at the time of enrollment.
Participants must have severe hemophilia A or B (FVIII <1% or FIX ≤2%) as evidenced by a central laboratory measurement at screening or documented medical record evidence.
Inhibitor titer of ≥0.6 BU/mL at screening, OR
Inhibitor titer of <0.6 BU/mL at screening with medical record evidence of 2 consecutive titers ≥0.6 BU/mL, OR
Known co-existing bleeding disorders other than hemophilia A or B.
Presence of clinically significant liver disease.
History of antiphospholipid antibody syndrome.
History of arterial or venous thromboembolism, unrelated to an indwelling venous access
Parallel
Fitusiran
DrugPharmaceutical form: solution for injection in PBS Route of administration: subcutaneous
Clotting factor concentrates (CFC) or bypassing agents (BPA)
Biological/VaccinePharmaceutical form: solution for injection Route of administration: intravenous injection
Antithrombin concentrate (ATIIIC)
Biological/VaccinePharmaceutical form: solution for injection Route of administration: intravenous injection
Annualized treated bleeding rate (ABR) in the fitusiran primary efficacy period and in the SOC period
A bleeding episode is defined as any occurrence of hemorrhage that requires administration of CFCs or BPAs
Annualized spontaneous bleeding rate (AsBR) in the fitusiran primary efficacy period and in the SOC period
A spontaneous bleeding episode is a bleeding event that occurs for no apparent or known reason, particularly into the joints, muscles, and soft tissues
Annualized joint bleeding rate (AjBR) in the fitusiran primary efficacy period and in the SOC period
A joint bleeding episode is characterized by an unusual sensation in the joint ("aura") in combination with 1) increasing swelling or warmth over the skin over the joint, 2) increasing pain, or 3) progressive loss of range of motion or difficulty in using the limb as compared with baseline
ABR in the fitusiran treatment period (160 weeks) for fitusiran-naïve participants
A bleeding episode is defined as any occurrence of hemorrhage that requires administration of CFCs or BPAs
ABR in the fitusiran treatment period (60 weeks) for rolled-over participants
A bleeding episode is defined as any occurrence of hemorrhage that requires administration of CFCs or BPAs
