Pharmacotherapeutic group: antihaemorrhagics, blood coagulation factor IX, ATC code: B02BD04.
Mechanism of action
Refixia is a purified recombinant human factor IX (rFIX) with a 40 kDa polyethylene-glycol (PEG) conjugated to the protein. The average molecular weight of Refixia is approximately 98 kDa and the molecular weight of the protein moiety alone is 56 kDa. Upon activation of Refixia, the activation peptide including the 40 kDa polyethylene-glycol moiety is cleaved off, leaving the native activated factor IX molecule.
Factor IX is a single chain glycoprotein. It is a vitamin-K dependent coagulation factor and it is synthesised in the liver. Factor IX is activated by factor XIa and by factor VII/tissue factor complex. Activated factor IX, in combination with activated factor VIII, activates factor X. Activated factor X converts prothrombin into thrombin. Thrombin then converts fibrinogen into fibrin and a clot is formed. Haemophilia B is a sex-linked hereditary disorder of blood coagulation due to decreased levels of factor IX and results in profuse bleeding into joints, muscles, or internal organs, either spontaneously or as a result of accidental or surgical trauma. By replacement therapy the plasma levels of factor IX are increased, thereby enabling a temporary correction of the factor deficiency and correction of the bleeding tendencies.
Clinical efficacy
The clinical trial programme included one phase 1 trial and five phase 3 multicentre, non-controlled trials. All patients had severe (factor IX level < 1%) or moderately severe (factor IX level ≤ 2%) haemophilia B.
Of note, annualised bleeding rate (ABR) is not comparable between different factor concentrates and between different clinical trials.
Prophylaxis
One hundred one of the previously treated patients and previously untreated pateints across all age-groups were treated with a weekly prophylactic dose of 40 IU/kg where 40 (40%) of these patients had no bleeding episodes (see details below).
Pivotal trial
The pivotal trial included 74 adolescent (13–17 years) and adult (18–65 years) previously treated patients (PTPs). The trial included one open-label on-demand arm with treatment for approximately 28 weeks and two prophylaxis treatment arms with single-blind randomisation to either 10 IU/kg or 40 IU/kg once-weekly for approximately 52 weeks. When comparing the 10 IU/kg and 40 IU/kg treatments, the annualised bleeding rate for patients in the 40 IU/kg arm was found to be 49% lower than the bleeding rate (95% CI: 5%;73%) for patients in the 10 IU/kg arm (p<0.05).
The median (IQR) overall ABR in patients (13–65 years) treated with a prophylactic dose of 40 IU/kg once weekly was 1.04 (0.00; 4.01) whereas the traumatic ABR was 0.00 (0.00; 2.05), joint ABR was 0.97 (0.00; 2.07) and spontaneous ABR was 0.00 (0.00; 0.99).
In this pivotal trial in adolescent and adult patients, there were 70 breakthrough bleeding episodes for 16 out of 29 patients in the 40 IU/kg prophylaxis arm. The overall success rate for treatment of breakthrough bleeds was 97.1% (67 out of 69 evaluated bleeds). A total of 69 (98.6%) of the 70 bleeding episodes were treated with one injection. Bleeding episodes were treated with Refixia at 40 IU/kg for mild or moderate bleeds.
In 29 adult and adolescent patients treated, 13 patients with 20 target joints were treated for one year with a weekly prophylactic dose of 40 IU/kg. Eighteen out of these 20 joints (90%) were no longer considered target joints at the end of the trial.
On-demand treatment
In the pivotal trial there was a non-randomised arm where 15 patients were treated in an on-demand regimen with 40 IU/kg for mild or moderate bleeds and 80 IU/kg for severe bleeds. The overall success rate (defined as excellent or good) for treatment of bleeds was 95% with 98% of the bleeds treated with one or two injections.
Paediatric population
Previously treated patients (PTPs)
The efficacy and safety of Refixia for prophylaxis and treatment of bleeds were evaluated in an open-label, single arm, non-controlled phase 3 trial. In the main phase of the paediatric PTP trial, 25 patients initially enrolled at 0 to 12 years of age received routine prophylactic administration of Refixia 40 IU/kg once weekly for 52 weeks. The patients were stratified into two age groups; 12 patients were 0 to 6 years and 13 patients 7 to 12 years at the time of signing informed consent. Twenty-two patients continued on to the extension phase and out of those, 12 patients had up to 8 years of routine prophylactic treatment. Main efficacy results in patients ≤ 12 years separated by main and extension phase are summarised in table 4 according to the age at randomization. .
Table 4: Annualised Bleeding Rate (ABR) in the Paediatric PTP Trial - Main & Extension Phase
| | Main Phase | Extension Phase |
| Age of patient* | ≤ 6 years N=12 | 7-12 years N=13 | ≤ 6 years N=11 | 7-12 years N=11 |
| Mean treatment period (years) | 1.05 | 1.27 | 7.71 | 6.85 |
| Total ABR | | | | |
| Poisson-estimated mean (95% CI) | 0.87 (0.38; 2.01) | 1.88 (1.14; 3.09) | 0.62 (0.30; 1.32) | 0.75 (0.34; 1.80) |
| Median (IQR) | 0.00 (0.00; 3.00) | 2.00 (0.00; 6.51) | 0.31 (0.00; 1.40) | 0.40 (0.14; 1.55) |
Due to the long trial duration several patients crossed age-groups and 10 patients that were initially enrolled as ≤ 6 years also contributed to the age category of 7-12 years.
In the 7‑12 years age group, 10 patients transitioned to the 13‑17 years age group. Of these 3 patients further transitioned to the ≥18 years age group. Considering this actual age for the main and extension phase of the trial together, the overall median/poisson-estimated ABR was 0.55/1.02 (95% CI: 0.68; 1.54) in patients ≤ 6 years and 0.52/0.92 (95% CI: 0.47; 1.78) in patients 7-12 years. The median/poisson-estimated ABR was 0.00/0.20 (95% CI: 0.09; 0.47) and 0.00/0.22 (95% CI: 0.05; 0.92) for spontaneous bleeds as well as 0.53/0.82 (95% CI: 0.55; 1.23) and 0.33/0.64 (95% CI: 0.31; 1.31) for traumatic bleeds in patients ≤ 6 years and patients 7-12 years, respectively. Treatment success (defined as excellent or good response) was concluded for 88.6% and 92.0% of bleeding episodes that occurred during prophylaxis in patients ≤ 6 years and patients 7-12 years, respectively. Four out of 25 patients (16%) did not have any bleeds throughout the trial.The mean annual consumption for prophylaxis was 2209.3 (SD: 79.3) IU/kg and 2324.9 (SD: 83.5) IU/kg for patients ≤ 6 years and patients 7-12 years, respectively. Two patients had target joints at baseline, which were considered resolved during the main phase. None of the patients developed new target joints in the trial.
Previously untreated patients (PUPs)
The efficacy and safety of Refixia for prophylaxis and treatment of bleeds were evaluated in an open-label, single-arm multicentre non-controlled phase 3 trial. Of the 54 exposed patients (< 6 years old), 47 patients (87%) completed the main phase, and 42 patients (77.8%) completed the extension phase. Main efficacy results separated by main and extension phase are summarised in table 5.
Table 5: Annualised Bleeding Rate (ABR) in the Paediatric PUP Trial - Main and Extension Phase
| | Main Phase N=51 | Extension Phase N=46 |
| Mean treatment period (years) | 0.78 | 3.34 |
| Total ABR | | |
| Poisson-estimated mean (95% CI) | 0.78 (0.33 ; 1.82) | 0.69 (0.41 ; 1.15) |
| Median (IQR) | 0.00 (0.00 ; 1.02) | 0.20 (0.00 ; 0.71) |
The overall median ABR was 0.00 for spontaneous, traumatic, and joint bleeding episodes for main phase and 0.20 for extension phase. For the trials main and extension phase the median/poisson-estimated ABR was 0.33/0.71 (95% CI: 0.41; 1.22) for PUPs on prophylaxis. The poisson-estimated ABRs for spontaneous and traumatic bleeds were 0.13 (95% CI: 0.05; 0.37) and 0.56 (95% CI: 0.32; 0.98) throughout the trial period, respectively (the median ABRs was 0 for both).47.8% of PUPs did not experience any bleeding events. None of the paediatric patients developed target joints in the trial. Out of 200 bleeds, 194 (97.0%) were successfully treated, achieving an excellent or good outcome and 182 (91.0%) were treated with a single injection. Of the 194 successfully treated bleeds, 92.8% required only one injection of Refixia for successful treatment.
Overall haemostatic efficacy
Bleeding episodes were treated with Refixia at 40 IU/kg for mild or moderate bleeds or 80 IU/kg for severe bleeds, where one bleed was evaluated as severe. An overall assessment of haemostatic efficacy was performed by the patient or caretaker (for home treatment) or study site investigator (for treatment under health care professional supervision) using a 4-point scale of excellent, good, moderate, or poor. The overall success rate (defined as excellent or good) for treatment of bleeds in previously treated patients was 91.6% (645 out of 704). Of the 704 treated bleeds observed in 85 (80.9%) of the 105 patients, 608 (86.4%) of the bleeds were resolved with 1 injection and 72 (10.2%) of the bleeds were resolved with 2 injections of Refixia
The success rate and dose needed for treatment of the bleeding episodes were independent of the localisation of the bleed. The success rate for treatment of bleeding episodes was also independent of whether the bleed was traumatic or spontaneous of nature.
Surgery
Five trials, of which one trial was a dedicated surgery trial, included in total 20 major and 105 minor surgery procedures . Haemostatic effect of Refixia during surgery was confirmed with a success rate of 100% in the 20 major surgeries in the trials. All evaluated minor surgeries were performed successfully.
In a dedicated surgery trial, the efficacy analysis included 13 major surgical procedures performed in 13 previously treated adult and adolescent patients. The procedures included 9 orthopaedic, 1 gastrointestinal, and 3 surgeries in the oral cavity. The patients received 1 pre-operative injection of 80 IU/kg on the day of surgery, and post-operatively, injections of 40 IU/kg. A pre-operative dose of 80 IU/kg Refixia was effective and no patients required additional doses on the day of surgery. In the post-surgery period Day 1 to 6 and Day 7 to 13, the median number of additional 40 IU/kg doses administered was 2.0 and 1.5, respectively. The mean total consumption of Refixia during and after surgery was 241 IU/kg (range: 81–460 IU/kg).