CLINICAL PHARMACOLOGY
Mechanism Of Action
The major pharmacologic actions of treprostinil are
direct vasodilation of pulmonary and systemic arterial vascular beds,
inhibition of platelet aggregation, and inhibition of smooth muscle cell
proliferation.
Pharmacodynamics
In a clinical trial of 240 healthy adult volunteers,
single doses of inhaled treprostinil 54 μg (the target clinical dose) and
84 μg (supratherapeutic inhalation dose) prolonged the corrected QTc
interval by approximately 10 msec. The QTc effect dissipated rapidly as the
concentration of treprostinil decreased. Orenitram has not been evaluated in a
thorough QTc study.
Pharmacokinetics
In patients with PAH, pharmacokinetics of treprostinil is
dose-proportional for systemic exposure (AUC0-t) over the dose range of 0.5 and
15 mg BID. Upon repeat administration with a BID regimen, the accumulation in
the systemic exposures to treprostinil is minimal and results in a
peak-to-trough ratio of approximately 7. However, a TID regimen will reduce the
peak-to-trough fluctuations to approximately 2.5 for the same total daily dose.
Absorption
The absolute oral bioavailability of Orenitram is
approximately 17%. Maximum treprostinil concentrations occur between
approximately 4 and 6 hours following Orenitram administration. Time to reach
steady-state concentrations for both BID and TID regimens is approximately 1 to
2 days.
The absorption of Orenitram is affected by food. The
AUCinf of treprostinil was increased by 49% and the Cmax was increased by an average
of 13% when Orenitram was administered following a high-fat, high-calorie meal
compared to fasting conditions in healthy volunteers. The relative
bioavailability of treprostinil following oral administration of Orenitram 1 mg
is not significantly altered by meal types ranging from 250 to 500 calories in
healthy volunteers.
When Orenitram 1 mg was administered with alcohol at 0.5
mg/kg or the equivalent of 3 servings (at the same time, or ± 1 hour relative
to alcohol consumption), there was no significant change (10% to 20% increase)
in the exposure to treprostinil compared to Orenitram administered alone.
Distribution
The treprostinil component of Orenitram is highly bound
to human plasma proteins, approximately 96% over a treprostinil concentration
range of 0.01-10 μg/mL.
Metabolism And Excretion
In a study conducted in healthy volunteers using [14C]
treprostinil, treprostinil was extensively metabolized on the side chain of the
molecule via oxidation, oxidative cleavage, dehydration, and glucuronic acid
conjugation. Treprostinil is primarily metabolized by CYP2C8 and to a lesser
extent by CYP2C9. No new metabolites are found upon oral administration
compared to parenteral administration of treprostinil. Only 1.13% and 0.19% is
excreted as unchanged parent drug in the feces and urine, respectively. Based
on in vitro studies treprostinil does not inhibit or induce major CYP enzymes
[see DRUG INTERACTIONS].
Specific Populations
Hepatic Impairment: In subjects with mild (n=8)
hepatic impairment, administration of a single 1 mg dose of Orenitram resulted
in a mean Cmax and an AUC0-inf that were 1.6- and 2.1-fold, respectively values
seen in healthy subjects. With moderate impairment (n=8), the corresponding
ratios were 4.0- and 4.8-fold, and with severe impairment (n=6), they were 4.8-
and 7.6-fold [see DOSAGE AND ADMINISTRATION, CONTRAINDICATIONS,
and Use in Specific Populations].
Renal Impairment: In patients with severe renal
impairment requiring dialysis (n=8), administration of a single 1 mg dose of
Orenitram pre- and post-dialysis resulted in an AUC0-inf that was not
significantly altered compared to healthy subjects.
Drug Interactions
Results of drug interaction studies are shown in Figure
1. Only for the strong CYP2C8 inhibitor does the interaction affect dosing [see
DOSAGE AND ADMINISTRATION].
Figure 1: Impact of Co-Administered Drugs on the
Systemic Exposure of Treprostinil 1 mg Compared to Orenitram Administered Alone
Warfarin: A drug interaction study was carried out
with Remodulin co-administered with warfarin (25 mg/day) in healthy volunteers.
There was no clinically significant effect of either medication on the
pharmacokinetics of treprostinil. Additionally, treprostinil did not affect the
pharmacokinetics or pharmacodynamics of warfarin. The pharmacokinetics of R-
and S- warfarin and the international normalized ratio (INR) in healthy
subjects given a single 25 mg dose of warfarin were unaffected by continuous
subcutaneous infusion of treprostinil at an infusion rate of 10 ng/kg/min
Clinical Studies
Clinical Trials In Pulmonary Arterial Hypertension (PAH)
Three multi-center, randomized, double-blind studies were
conducted and compared Orenitram to placebo in a total of 349 (Study 1), 350
(Study 2), and 310 (Study 3) patients with PAH.
Study 1 (Effect Seen With no Background Vasodilator)
Study 1 was a 12-week, randomized (2:1 Orenitram to
placebo), double-blind, placebo-controlled, international efficacy and safety
study of Orenitram in patients with WHO Group 1 PAH not currently receiving PAH
therapy. The primary efficacy endpoint was placebo-corrected change in
six-minute walk distance (6MWD) from Baseline to Week 12. Study drug dose was
titrated to a maximum of 12 mg BID based on clinical response and study drug
tolerability. Study 1 enrolled 349 patients (overall analysis population) who
were not receiving any PAH medication. At the beginning of the study, subjects
were dosed with only the 1 mg tablets with 0.5 and 0.25 mg tablets introduced
at sequentially later dates during the study. The primary analysis population
consisted of the 228 patients who had access to the 0.25 mg tablet at the time
of randomization. Patients were administered Orenitram or placebo twice daily,
with the doses titrated to effect over the course of the 12-week trial.
Patients were in WHO functional class II (~33%) and class III (~66%) with
either idiopathic or heritable PAH (~75%), collagen vascular disease associated
PAH (~19%), or PAH associated with HIV (1%) or congenital heart defect (5%) or
other conditions (~6%). The patients' mean baseline 6MWD was approximately 330
meters. In the primary analysis population, 17% of patients discontinued
Orenitram compared to 14% of patients on placebo.
The primary efficacy endpoint of the trial was the change
in 6MWD at 12 weeks for the primary analysis population. Analysis of Study 1
results demonstrated that those patients receiving Orenitram compared to
patients receiving placebo improved their median 6MWD by approximately +23
meters (Hodges-Lehmann estimate; p=0.013, non-parametric analysis of covariance
in accordance with the pre-specified statistical analysis plan) as compared to
patients receiving placebo as demonstrated in (Figure 2). The within group
median change from baseline was +25 meters for Orenitram and -5 meters for
placebo at week 12 (N=228). Mean dose (±SD) in the Orenitram group was 2.3 ±
1.3, 3.2 ± 1.9, and 3.4 ± 1.9 mg BID at Weeks 4, 8, and 12, respectively with a
maximum dose of 12 mg BID. The distribution of the 6MWD change from baseline at
Week 12 was also plotted across the range of observed values (Figure 3).
Figure 2: Hodges-Lehmann Estimate of Treatment Effect
by Visit for the Primary Analysis Population (Study 1)
Figure 3: Plot of the Distribution of Peak 6MWD
Changes at Week 12 for the Primary Analysis Population (Study 1)
The placebo-corrected median treatment effect on 6MWD was
estimated (using the Hodges Lehmann estimator) within various subpopulations
defined by age, gender, disease etiology, and baseline 6MWD (Figure 4).
Figure 4: Placebo Corrected Median Treatment Effect
(Hodges-Lehmann estimate with 95% CI) on 6MWD Change from Baseline at Week 12
for Various Subgroups in the Primary Analysis Population (Study 1)
Studies 2 and 3 (no effect on a background of ERA, PDE5
inhibitor, or both)
Studies 2 (N=350) and 3 (N=310) were 16-week, randomized,
double-blind, placebo-controlled, international efficacy and safety studies of
Orenitram in patients with WHO Group 1 PAH. The primary efficacy endpoint was
placebo-corrected change in 6MWD from Baseline to Week 16. Patients were in WHO
functional class II (~23%) and class III (~77%) with either idiopathic or
heritable PAH (~66%), collagen vascular disease associated PAH (~29%), or PAH
associated with HIV (1%) or congenital heart defect (4%). The patients' mean
baseline 6MWD was approximately 340 meters. Approximately 40% were receiving
both an ERA and a PDE5 inhibitor. The results did not demonstrate a benefit in
exercise testing with median 6MWD at Week 16 (11 meters [Hodges-Lehmann
estimate; p=0.072] and 10 meters [Hodges-Lehmann estimate; p=0.089],
respectively).
Long-Term Treatment Of Pulmonary Hypertension
Patients (N=824) from the placebo-controlled studies
entered a long-term, uncontrolled, openlabel extension study. The average
exposure to Orenitram was approximately 2 years with a maximum exposure of
approximately 6 years. The dose of Orenitram continued to increase over time
with doses (mean ± SD) of 3.6 ± 2.7, 4.2 ± 3.1, and 5 ± 3.7 mg BID at 6
(n=649), 12 (n=433), and 24 months (n=238), respectively, with a maximum dose
of 21 mg BID. Reasons for discontinuation from the study included adverse event
(16%), progression of disease (15%), death (13%), and withdrawn consent (7%).
In the 522 subjects that completed the 12-month efficacy assessment, their mean
6MWD improved by 24 meters compared to baseline (30 meters in monotherapy
patients and 20 meters when Orenitram was used in combination with an ERA
and/or a PDE-5 inhibitor). Of the patients that remained in the study, overall
survival was 92%, 87%, and 82% at the end of 1, 2, and 3-years, respectively,
with progression-free survival (progression defined as death, discontinuation
or addition of a PAH therapy) of 74%, 61%, and 47%. Without a control group,
these data must be interpreted cautiously.
Remodulin To Orenitram Transition Study
A 24-week, multicenter, open-label study enrolled 33 WHO
Group 1 patients on stable doses of Remodulin. All patients received background
therapy with a PDE-5 inhibitor and/or ERA. Patients were WHO Functional Class I
or II and hemodynamically stable at baseline with a cardiac index > 2.2 L/m²,
RAP < 11 mmHg, and PVR < 10 Woods units. The primary endpoint of the study
was the safety and tolerability of the transition. Successful transition was
defined as transition from Remodulin to Orenitram at Week 4 (no longer
receiving Remodulin) and clinically maintained on Orenitram through Week 24 (as
measured by 6MWD and hemodynamics).
All patients transitioned from Remodulin to Orenitram
(median time to transition of 3 days;) with thirty-one patients (94%)
completing transition in 5 days (range 2 to 29 days).Two subjects discontinued
Orenitram. The mean Orenitram total daily dose at the end of transition was 27
mg ± 12 mg compared to a mean Remodulin dose prior to transition of 59
ng/kg/min (25 to 111 ng/kg/min). The mean Orenitram total daily dose at Week 24
was 36 mg ± 16 mg.After 24 weeks of treatment with Orenitram, 6MWD and
hemodynamics remained stable. Without a control group, these data must be
interpreted cautiously.