CLINICAL PHARMACOLOGY
Mechanism Of Action
Avatrombopag is an orally
bioavailable, small molecule TPO receptor agonist that stimulates proliferation
and differentiation of megakaryocytes from bone marrow progenitor cells
resulting in an increased production of platelets. Avatrombopag does not
compete with TPO for binding to the TPO receptor and has an additive effect
with TPO on platelet production.
Pharmacodynamics
Platelet Response
Avatrombopag resulted in
dose-and exposure-dependent elevations in platelet counts in adults. The onset
of the platelet count increase was observed within 3 to 5 days of the start of
a 5-day treatment course, with peak effect observed after 10 to 13 days.
Subsequently, platelet counts decreased gradually, returning to near baseline
values after 35 days.
Cardiac Electrophysiology
At exposures similar to that
achieved at the 40 mg and 60 mg dose, DOPTELET does not prolong the QT interval
to any clinically relevant extent. Mean QTc prolongation effects >20 ms are
not anticipated with the highest recommended therapeutic dosing regimen based
on analysis of data from the pooled clinical trials in patients with chronic
liver disease.
Pharmacokinetics
Avatrombopag demonstrated
dose-proportional pharmacokinetics after single doses from 10 mg (0.25-times
the lowest approved dosage) to 80 mg (1.3-times the highest recommended
dosage). Healthy subjects administered 40 mg of avatrombopag had a geometric
mean (%CV) maximal concentration (Cmax) of 166 (84%) ng/mL and area under the
time-concentration curve extrapolated to infinity (AUC0-inf) of 4198 (83%)
ng.hr/mL. The pharmacokinetics of avatrombopag were similar in both healthy
subjects and the chronic liver disease population.
Absorption
The median time to maximal concentration (Tmax) occurred
at 5 to 6 hours post-dose.
Effect Of Food
Avatrombopag AUC0-inf and Cmax were not affected when
DOPTELET was co-administered with a low-fat meal (500 calories, 3 g fat, 15 g
proteins, and 108 g carbohydrates) or a high-fat meal (918 calories, 59 g fat,
39 g proteins, and 59 g carbohydrates). The variability of avatrombopag
exposure was reduced by 40% to 60% with food. The Tmax of avatrombopag was
delayed by 0 to 2 hours when DOPTELET was administered with a low-fat or
high-fat meal (median Tmax range 5 to 8 hours) compared to the fasted state.
Distribution
Avatrombopag has an estimated mean volume of distribution
(%CV) of 180 L (25%). Avatrombopag is greater than 96% bound to human plasma
proteins.
Elimination
The mean plasma elimination half-life (%CV) of
avatrombopag is approximately 19 hours (19%). The mean (%CV) of the clearance
of avatrombopag is estimated to be 6.9 L/hr (29%).
Metabolism
Avatrombopag is primarily metabolized by cytochrome P450
(CYP) 2C9 and CYP3A4.
Excretion
Fecal excretion accounted for 88% of the administered
dose, with 34% of the dose excreted as unchanged avatrombopag. Only 6% of the
administered dose was found in urine.
Specific Populations
Age (18-86 years), body weight (39-175 kg), sex, race
[Whites, African Americans, and East Asians (i.e., Japanese, Chinese and
Koreans)], and any hepatic impairment (Child-Turcotte-Pugh (CTP) grade A, B,
and C, or Model for End-Stage Liver Disease (MELD) score 4-23) and mild to
moderate renal impairment (CLcr ≥30 mL/min) did not have clinically
meaningful effects on the pharmacokinetics of avatrombopag.
The effect of age (< 18 years) and severe renal
impairment (CLcr < 30 mL/min, Cockcroft-Gault) including patients requiring
hemodialysis on avatrombopag pharmacokinetics is unknown.
Drug Interactions
Drug interaction studies were performed in healthy
subjects with single 20 mg DOPTELET dose and drugs likely to be co-administered
or drugs commonly used as probes for pharmacokinetic interactions (see Table
3).
Table 3: Drug Interactions: Changes in
Pharmacokinetics of Avatrombopag in the Presence of Co-administered Drug
Co-administered Drug* |
Geometric Mean Ratio [90% CI] of Avatrombopag PK with/without Coadministered Drug (No Effect=1.00) |
AUC0-inf |
Cmax |
Strong CYP3A Inhibitor |
Itraconazole |
1.37 (1.10, 1.72) |
1.07 (0.86, 1.35) |
Moderate CYP3A and CYP2C9 Inhibitor |
Fluconazole |
2.16 (1.71, 2.72) |
1.17 (0.96, 1.42) |
Moderate CYP2C9 and Strong CYP3A Inducer |
Rifampin |
0.57 (0.47, 0.62) |
1.04 (0.88, 1.23) |
P-gp Inhibitor |
Cyclosporine |
0.83 (0.65, 1.04) |
0.66 (0.54, 0.82) |
P-gp and Moderate CYP3A Inhibitor |
Verapamil |
1.61 (1.21, 2.15) |
1.26 (0.96, 1.66) |
* at steady state, except for cyclosporine which was
administered as a single dose |
Effect Of Avatrombopag
Avatrombopag does not inhibit
CYP1A, CYP2B6, CYP2C8, CYP2C9, CYP2C19, CYP2D6, CYP2E1, or CYP3A, does not
induce CYP1A, CYP2B6, CYP2C, and CYP3A, and weakly induces CYP2C8 and CYP2C9 in
vitro.
Avatrombopag inhibits organic
anion transporter (OAT) 3 and breast cancer resistance protein (BCRP) but not
organic anion transporter polypeptide (OATP) 1B1 and 1B3, organic cation
transporter (OCT) 2, and OAT1 in vitro.
Effect Of Transporters
Avatrombopag is a substrate for
P-glycoprotein (P-gp) mediated transport [see Table 3]. Avatrombopag is not a
substrate for OATP1B1, OATP1B3, OCT2, OAT1, and OAT3.
Clinical Studies
The efficacy of DOPTELET for the treatment of
thrombocytopenia in patients with chronic liver disease who are scheduled to
undergo a procedure was established in 2 identically-designed multicenter,
randomized, double-blind, placebo-controlled trials (ADAPT-1 (NCT01972529) and
ADAPT-2 (NCT01976104)). In each study, patients were assigned to the Low
Baseline Platelet Count Cohort (<40 x109L) or the High Baseline
Platelet Count Cohort (≥40 to <50 x109 L) based on their
platelet count at Baseline. Patients were then randomized in a 2:1 ratio to
either DOPTELET or placebo. Patients were stratified according to
hepatocellular cancer (HCC) status and risk of bleeding associated with the
elective procedure (low, moderate, or high). Patients undergoing neurosurgical
interventions, thoracotomy, laparotomy or organ resection were not eligible for
enrollment.
Patients in the Low Baseline Platelet Count Cohort
received 60 mg DOPTELET or matching placebo once daily for 5 days, and patients
in the High Baseline Platelet Count Cohort received 40 mg DOPTELET or
matching placebo once daily for 5 days. Eligible patients were scheduled to
undergo their procedure (low, moderate, or high bleeding risk) 5 to 8 days
after their last dose of treatment. Patient populations were similar between
the pooled Low and High Baseline Platelet Count Cohorts and
consisted of 66% male and 35% female; median age 58 years and 61% White, 34%
Asian, and 3% Black.
In ADAPT-1, a total of 231 patients were randomized, 149
patients were treated with DOPTELET and 82 patients were treated with placebo.
In the Low Baseline Platelet Count Cohort, the mean Baseline platelet
count for the DOPTELET-treated group was 31.1 x109/L and for placebo-treated patients
was 30.7 x109/L. In the High Baseline Platelet Count Cohort, the mean
Baseline platelet count for the DOPTELET-treated patients was 44.3 x109/L and
for placebo-treated patients was 44.9 x109/L.
In ADAPT-2, a total of 204 patients were randomized, 128
patients were treated with DOPTELET and 76 patients were treated with placebo.
In the Low Baseline Platelet Count Cohort, the mean Baseline platelet
count for the DOPTELET-treated group was 32.7 x109/L and for placebo-treated
patients was 32.5 x109/L. In the High Baseline Platelet Count Cohort,
the mean Baseline platelet count for the DOPTELET-treated patients was 44.3 x109/L
and for placebo-treated patients was 44.5 x109/L.
Across both baseline platelet count cohorts and the
avatrombopag and placebo treatment groups, patients underwent a broad spectrum
of types of scheduled procedures that ranged from low to high bleeding risk.
Overall, the majority of patients (60.8% [248/430] subjects) in all treatment
groups underwent low bleeding risk procedures, 17.2% [70/430] of patients
underwent procedures associated with moderate bleeding risk, and 22.1% [90/430]
of subjects underwent procedures associated with high bleeding risk. The
proportions of patients undergoing low, moderate, and high-risk procedures were
similar between the avatrombopag and placebo treatment groups.
The major efficacy outcome was the proportion of patients
who did not require a platelet transfusion or any rescue procedure for bleeding
after randomization and up to 7 days following an elective procedure.
Additional secondary efficacy outcomes were the proportion of patients who
achieved platelet counts of >50 x109/L on the day of procedure and the
change in platelet count from baseline to procedure day.
Responders were defined as patients who did not require a
platelet transfusion or any rescue procedure for bleeding after randomization
and up to 7 days following a scheduled procedure. The following were considered
rescue therapies to manage risk of bleeding associated with a procedure: whole
blood transfusion, packed red blood cell (RBC) transfusion, platelet
transfusion, fresh frozen plasma (FFP) or cryoprecipitate administration,
Vitamin K, desmopressin, recombinant activated factor VII, aminocaproic acid,
tranexamic acid, or surgical or interventional radiology procedures performed
to achieve hemostasis and control blood loss. In both baseline platelet count
cohorts, patients in the DOPTELET treatment groups had a greater proportion of
responders than the corresponding placebo treatment groups that was both
clinically meaningful and statistically significant as detailed in Table 4.
Table 4: Proportion of Subjects Not Requiring a
Platelet Transfusion or Any Rescue Procedure for Bleeding by Baseline Platelet
Count Cohort and Treatment Group – ADAPT-1 and ADAPT-2
Low Baseline Platelet Count Cohort (<40 x109/L) |
Category |
ADAPT-1 |
ADAPT-2 |
DOPTELET 60 mg
(n=90) |
Placebo
(n=48) |
DOPTELET 60 mg
(n=70) |
Placebo
(n=43) |
Responders |
66% |
23% |
69% |
35% |
95% CIa |
(56, 75) |
(11, 35) |
(58, 79) |
(21, 49) |
Difference of Proportion vs. Placebob |
43% |
34% |
95% CIc |
(27, 58) |
(16, 52) |
p-valued |
<0.0001 |
0.0006 |
High Baseline Platelet Count Cohort (≥40 to <50 x109/L) |
Category |
ADAPT-1 |
ADAPT-2 |
DOPTELET 40 mg
(n=59) |
Placebo
(n= 34) |
DOPTELET 40 mg
(n=58) |
Placebo
(n=33) |
Responders |
88% |
38% |
88% |
33% |
95% CIa |
(80, 96) |
(22, 55) |
(80, 96) |
(17, 49) |
Difference of Proportion vs. Placebob |
50% |
55% |
95% CIc |
(32, 68) |
(37, 73) |
p-valued |
<0.0001 |
<0.0001 |
a Two-sided 95% confidence interval based on
normal approximation.
b Difference of proportion vs. placebo = proportion of Responders
for DOPTELET – proportion of Responders for placebo
c 95% confidence interval calculated based on normal approximation.
d By Cochran-Mantel-Haenszel Testing stratified by bleeding risk for
the procedure. |
In addition, both trials demonstrated a higher proportion
of patients who achieved the target platelet count of ≥ 50 x109/L on the
day of the procedure, a secondary efficacy endpoint, in both DOPTELET-treated
groups versus the placebo-treated groups for both cohorts (Low Baseline
Platelet Count Cohort-ADAPT-1: 69% vs 4%, respectively; P <0.0001;
ADAPT-2: 67% vs 7%, respectively; P <0.0001; High Baseline Platelet Count
Cohort-ADAPT-1: 88% vs 21%, respectively; P <0.0001; ADAPT-2: 93% vs
39%, respectively; P <0.0001).
Further, both trials
demonstrated a greater mean change in platelet counts from baseline to the day
of the procedure, a secondary efficacy endpoint, in both DOPTELET-treated
groups versus the placebo-treated groups for both cohorts (Low
Baseline Platelet Count Cohort-ADAPT-1: 32 x109/L vs 0.8 x109/L,
respectively; P <0.0001; ADAPT-2: 31.3 x109/L vs 3.0 x109/L, respectively; P
<0.0001; High Baseline Platelet Count Cohort-ADAPT-1: 37.1 x109/L vs
1.0 x109/L, respectively; P <0.0001;ADAPT-2: 44.9 x109/L vs 5.9 x109/L,
respectively; P <0.0001).
A measured increase in platelet counts was observed in
both DOPTELET treatment groups over time beginning on Day 4 post-dose, that
peaked on Day 10-13, decreased 7 days post-procedure, and then returned to near
baseline values by Day 35.