CLINICAL PHARMACOLOGY
Mechanism Of Action
AFSTYLA is a recombinant protein that replaces the
missing Coagulation Factor VIII needed for effective hemostasis. AFSTYLA is a
single polypeptide chain with a truncated B-domain that allows for a covalent
bridge to link the Factor VIII heavy and light chains. AFSTYLA has demonstrated
a higher VWF affinity relative to full-length rFVIII.1 VWF stabilizes Factor
VIII and protects it from degradation. Activated AFSTYLA has an amino acid
sequence identical to endogenous FVIIIa.
Pharmacodynamics
Hemophilia A is an X-linked hereditary disorder of blood
coagulation due to decreased levels of Factor VIII and results in bleeding into
joints, muscles or internal organs, either spontaneously or as result of accidental
or surgical trauma. Replacement therapy increases the plasma levels of Factor
VIII enabling a temporary correction of the factor deficiency and correction of
the bleeding tendencies.
Pharmacokinetics
Subjects ≥ 12 years
The pharmacokinetics (PK) of AFSTYLA were evaluated in 91
(81 adults ≥ 18 years and 10 adolescents ≥ 12 to < 18 years)
previously treated subjects following an intravenous injection of a single dose
of 50 IU/kg.
The PK parameters (Table 5) were based on plasma Factor
VIII activity measured by the chromogenic assay after the first dose (initial
PK assessment). The PK profile obtained 3 to 6 months after the initial PK
assessment was comparable with the PK profile obtained after the first dose.
Table 5: Pharmacokinetic Parameters (Arithmetic Mean,
Coefficient of Variation [CV%]) in Adults and Adolescents Following a Single Injection
of 50 IU/kg of AFSTYLA - Chromogenic Assay
PK Parameters |
≥ 18 years
(N=81) |
≥ 12 to < 18 years
(N=10) |
IR (IU/dL)/(IU/kg) |
2.00 (20.8) |
1.69 (24.8) |
Cmax (IU/dL) |
106 (18.1) |
89.7 (24.8) |
AUC0-inf (IU*h/dL) |
1960 (33.1) |
1540 (36.5) |
t½ (h) |
14.2 (26.0) |
14.3 (33.3) |
MRT (h) |
20.4 (25.8) |
20.0 (32.2) |
CL (mL/h/kg) |
2.90 (34.4) |
3.80 (46.9) |
Vss (mL/kg) |
55.2 (20.8) |
68.5 (29.9) |
IR = incremental recovery recorded at 30 minutes after
injection; Cmax = observed maximum plasma concentration; AUC0-inf = area under
the Factor VIII activity time curve extrapolated to infinity; t½ = half-life;
MRT = mean residence time; CL = body weight adjusted clearance; Vss = body
weight adjusted volume of distribution at steady-state. |
Children < 12 years
Pharmacokinetic parameters of AFSTYLA were evaluated in
39 previously treated children (0 to < 12 years) in open-label, multicenter
studies following a 50 IU/kg intravenous injection of AFSTYLA.
Table 6 summarizes the PK parameters calculated from the
pediatric data. These parameters were estimated based on the plasma Factor VIII
activity over time profile.
Table 6: Comparison of Pharmacokinetic Parameters in
Children by Age Category (Arithmetic Mean, Coefficient of Variation [CV%])
Following a Single Injection of 50 IU/kg of AFSTYLA - Chromogenic Assay
PK Parameters |
0 to < 6 years
(N=20) |
≥ 6 to < 12 years
(N=19) |
IR (IU/dL)/(IU/kg) |
1.60 (21.1) |
1.66 (19.7) |
Cmax (IU/dL) |
80.2 (20.6) |
83.5 (19.5) |
AUC0-inf (IU*h/dL) |
1080 (31.0) |
1 170 (26.3) |
t½ (h) |
10.4 (28.7) |
10.2 (19.4) |
MRT (h) |
12.4 (25.0) |
12.3 (16.8) |
CL (mL/h/kg) |
5.07 (29.6) |
4.63 (29.5) |
Vss (mL/kg) |
71.0 (11.8) |
67.1 (22.3) |
IR = incremental recovery recorded at 30 minutes after
injection for subjects 12 to < 18 years and at 60 minutes after injection
for subjects 1 to < 12 years; Cmax = observed maximum plasma concentration;
AUC = area under the Factor VIII activity time curve extrapolated to infinity;
t½ = half-life; MRT = mean residence time; CL = body weight adjusted clearance;
Vss = body weight adjusted volume of distribution at steady-state. |
Clinical Studies
The safety and efficacy of AFSTYLA were evaluated in two
studies: an Open-label, Multicenter, Crossover Safety, Efficacy and
Pharmacokinetic Study in adults/adolescents as well as in an Open-label
Pharmacokinetic, Efficacy and Safety study in children. These studies
characterized the PK of AFSTYLA and determined hemostatic efficacy in the
control of bleeding events, the prevention of bleeding events in prophylaxis
and in the adult/ adolescent study determined hemostatic efficacy during
perioperative management of bleeding in subjects undergoing surgical
procedures.
The adult/adolescent study enrolled a total of 175
previously treated male subjects with severe hemophilia A ( < 1% endogenous
Factor VIII activity). Subjects ranged in age from 12 to 65 years, including 14
adolescent subjects ( ≥ 12 to < 18 years). Of the 175 enrolled subjects,
174 received at least one dose of AFSTYLA and 173 (99%) were evaluable for efficacy.
A total of 161 subjects (92.5%) completed the study. A total of 120 (69.0%) subjects
were treated for at least 50 EDs and 52 (29.9%) of those subjects were treated for
at least 100 EDs. Subjects received a total of 14,592 injections with a median
of 67.0 (range 1 to 395) injections per subject.
The pediatric study enrolled 84 previously treated male
subjects with severe hemophilia A (35 subjects 0 to < 6 years and 49 subjects
≥ 6 to < 12 years). Of the 84 enrolled subjects, all received at least
one dose of AFSTYLA and 83 (99%) were evaluable for efficacy. A total of 65
(77.4%) subjects were treated for at least 50 EDs and 8 (9.5%) of those
subjects were treated for at least 100 EDs. Subjects received a total of 5,313
injections with a median of 59 (range 4 to 145) injections per subject.
On-demand Treatment And Control Of Bleeding Episodes
In the adult/adolescent study a total of 848 bleeding
episodes were treated with AFSTYLA and 835 received an efficacy assessment by
the investigator. The majority of the bleeding episodes occurred in joints. The
median dose per injection used to treat a bleeding episode was 31.7 IU/kg
(range 6 to 84 IU/kg). Of the 848 bleeding episodes, 686 (81%) were controlled
with a single AFSTYLA injection and another 107 (13%) were controlled with 2 injections.
Fifty-five (6%) of the 848 bleeding episodes required 3 or more injections. For
94% of bleeding episodes the hemostatic efficacy rating by the investigator was
either excellent or good.
In the pediatric study a total of 347 bleeding episodes
were treated with AFSTYLA all of which received an efficacy assessment by the
investigator. The majority of the bleeding episodes occurred in joints. The
median dose per injection used to treat a bleeding episode was 27.3 IU/kg
(range 16 to 76 IU/kg). Of the 347 bleeding episodes, 298 (86%) were controlled
with a single AFSTYLA injection and another 34 (10%) were controlled with 2
injections. Fifteen (4%) of the 347 bleeding episodes required 3 or more
injections. For 96% of bleeding episodes the hemostatic efficacy rating by the
investigator was either excellent or good.
Assessment of response to treatment of bleeds by the
investigator was as follows:
Excellent: Pain relief and/or improvement in signs
of bleeding (i.e., swelling, tenderness, and/or increased range of motion in
the case of musculoskeletal hemorrhage) within approximately 8 hours after the
first infusion
Good: Pain relief and/or improvement in signs of
bleeding at approximately 8 hours after the first infusion, but requires two
infusions for complete resolution
Moderate: Probable or slight beneficial effect
within approximately 8 hours after the first infusion; requires more than two
infusions for complete resolution
No response: No improvement at all or condition
worsens (i.e., signs of bleeding) after the first infusion and additional
hemostatic intervention is required with another FVIII product,
cryoprecipitate, or plasma for complete resolution.
Efficacy in control of bleeding episodes in both studies
is summarized in Table 7.
Table 7: Efficacy of AFSTYLA in Control of Bleeding
Bleeding Episodes Treated |
Adult and Adolescent ( ≥ 12 to 65 years of age)
(N=848) |
Pediatric (0 to < 12 years of age)
(N=347) |
Number of injections |
1 injection, n (%) |
686 (81%) |
298 (85.9%) |
2 injections, n (%) |
107 (13%) |
34 (9.8%) |
3 injections, n (%) |
29 (3%) |
8 (2.3%) |
> 3 injections, n (%) |
26 (3%) |
7 (2.0%) |
Efficacy evaluation by investigator |
(N=835) |
(N=347) |
Excellent or Good, n (%) |
783 (94%) |
334 (96.3%) |
Moderate, n (%) |
52 (6%) |
12 (3.5%) |
No response, n (%) |
0 |
1 (0.3%) |
Routine Prophylaxis
Adult and Adolescent Study
In the adult/adolescent and pediatric studies, subjects
received prophylaxis in a regimen that was determined by the investigator,
taking into account the subject's Factor VIII treatment regimen used prior to
enrollment and the subject's bleeding phenotype.
In the adult/adolescent study, 54% of the 146 subjects on
prophylaxis received AFSTYLA 3 times weekly; 32% of subjects received AFSTYLA 2
times weekly; 6% received AFSTYLA every other day, and 8% of subjects received
other regimens.
The annualized bleeding rate (ABR) was comparable between
subjects on a 3 times weekly regimen (median ABR of 1.53) and those on a 2
times weekly regimen (median ABR of 0.00). The annualized spontaneous bleeding
rate (AsBR) was also comparable between subjects on a 3 times weekly regimen
(median AsBR of 0.0) and those on a 2 times weekly regimen (median AsBR of
0.0). The number of subjects who needed dose adjustments was comparable between
the two groups (34.2% [27 subjects] for three times weekly and 27.7% [13
subjects] for twice weekly).
The median prescribed dose for subjects on a 3 times
weekly prophylaxis regimen was 30 IU/kg (12 to 50 IU/kg). The median prescribed
dose for subjects on a 2 times weekly regimen was 35 IU/kg (17 to 50 IU/kg).
The ABR in prophylaxis (median of 1.14) was significantly
lower (p < 0.0001) than the ABR that was observed in subjects treated
on-demand (median of 19.64). Sixty-three of 146 subjects (43%) experienced no
bleeding episodes while on prophylaxis. There were no severe or
life-threatening bleeds (e.g., intracranial hemorrhage) in subjects receiving prophylaxis.
Pediatric Study
In the pediatric study, 54% of the 80 subjects on
prophylaxis received AFSTYLA 2 times a week; 30% of subjects received AFSTYLA 3
times a week; 4% received AFSTYLA every other day, and 12% of subjects received
other regimens.
Twenty-one of 80 subjects (26%) experienced no bleeding
episodes while on prophylaxis. There was one severe bleed (hip joint
hemorrhage) in the pediatric study that was successfully treated.
For subjects on prophylaxis the overall ABR was 3.69,
with a median ABR of 2.30 for subjects on a 3 times a week regimen and 4.37 for
subjects on a 2 times a week regimen. The median AsBR (0.00) was identical
between subjects on the 3 times a week and 2 times a week regimens.
The median prescribed dose for subjects on a 3 times a
week regimen was 32 IU/kg (19 to 50 IU/kg) and for subjects on a 2 times a week
regimen was 35 IU/kg (20 to 57 IU/kg). The ABRs for prophylaxis and on-demand
in both studies are summarized in Table 8.
Table 8: Summary of Annualized Bleeding Rate (ABR) by
AFSTYLA Treatment Regimen
|
Phase I/III Adult/ Adolescent Study |
Phase III Pediatric Study |
Prophylaxis
(N=146) |
On-demand
(N=27) |
Prophylaxis
(N=80) |
On-demand
(N=3) |
Overall ABR Median (IQR*) |
1.14 (0-4.2) |
19.64 (6.2-46.5) |
3.69 (0-7.2) |
78.56 (35.1-86.6) |
Annualized Spontaneous Bleeding Rate (AsBR) Median (IQR*) |
0 (0-2.4) |
11.73 (2.8-36.5) |
0 (0-2.2) |
31.76 (0-42.7) |
Number of subjects with zero bleeding episodes |
63 (43.2%) |
1 (3.7%) |
21 (26.3%) |
0 |
* IQR = interquartile range, 25th percentile to 75th
percentile |
Perioperative Management Of Bleeding
Thirteen subjects in the adult/adolescent study underwent
a total of 16 surgical procedures. Overall, investigators assessed hemostatic
efficacy of AFSTYLA in perioperative management of bleeding as excellent in 15
of 16 surgeries and as good in 1 of 16 surgeries (see Table 9). Median factor
consumption pre- and intra-operatively was 89.4 IU/kg (range 40.5 to 108.6
IU/kg).
Assessment of hemostasis during surgical procedures by
the investigator was as follows:
Excellent: Hemostasis clinically not significantly
different from normal (e.g., achieved hemostasis comparable to that expected
during similar surgery in a non-factor deficient patient) in the absence of
other hemostatic intervention and estimated blood loss during surgery is not
more than 20% higher than the predicted blood loss for the intended surgery
Good: Normal or mildly abnormal hemostasis in
terms of quantity and/or quality (e.g., slight oozing, prolonged time to
hemostasis with somewhat increased bleeding compared to a non-factor deficient
patient in the absence of other hemostatic intervention) or estimated blood
loss is > 20%, but ≤ 30% higher than the predicted blood loss for
intended surgery
Moderate: Moderately abnormal hemostasis in terms
of quantity and/or quality (e.g., moderate hemorrhage that is difficult to
control) with estimated blood loss greater than what is defined as good
Poor/No Response: Severely abnormal hemostasis in
terms of quantity and/or quality (e.g., severe hemorrhage that is difficult to
control) and/or additional hemostatic intervention required with another FVIII
product, cryoprecipitate, or plasma for complete resolution.
Table 9: Efficacy of AFSTYLA in Perioperative
Management of Bleeding
Procedure |
Efficacy Evaluation |
Factor Consumption (IU/kg) (pre- and intra-operatively) |
Extraction of wisdom teeth |
Excellent |
51.09 |
Abdominal hernia repair |
Excellent |
47.89 |
Elbow replacement |
Excellent |
108.58 |
Ankle arthroplasty |
Excellent |
76.83 |
Knee replacement (5) |
Excellent (4), Good (1) |
92.49 |
100.9 |
67.26 |
105.79 |
86.09 |
Cholecystectomy and |
Excellent |
105.95 |
Lengthening of the Achilles tendon combined with: Straightening of the right toes |
Excellent |
|
Circumcision (3) |
Excellent (3) |
99.04 |
92.74 |
81.5 |
Open reduction internal fixation (ORIF) right ankle |
Excellent |
89.36 |
Hardware removal, Right ankle |
Excellent |
40.45 |
REFERENCES
1 Zollner S, Raquet E, Claar Ph, Müller-Cohrs J, Metzner
HJ, Weimer Th, Pragst I, Dickneite G, Schulte S. Non-clinical pharmacokinetics
and pharmacodynamics of rVIII-SingleChain, a novel recombinant single-chain
factor VIII, Thrombosis Research 2014; 134: 125-131.