Study design
This open label, phase IIIb, single-arm study was conducted from 21 December 2012 to 15 August 2014 at 12 centres in China. Following a 4-week screening period, eligible subjects received 5 mg ambrisentan orally once daily for a 12-week primary evaluation period. Subjects then proceeded to a 12-week dose adjustment period during which dose titration to 10 mg was allowed. The total duration of study was 28 weeks.
Study population
Chinese subjects of either gender, aged 18–75 years, diagnosed with PAH (WHO FC II or III) categorised in Group 1 of the WHO Updated Clinical Classification of Pulmonary Hypertension [
1] were enrolled in the study. All subjects had to perform the 6 min walk test (6MWT) with a minimum distance of 150 m and maximum distance of 450 m. Additionally, results from a right heart catherisation performed within 6 months of screening had to demonstrate mean pulmonary artery pressure ≥25 mmHg; pulmonary vascular resistance ≥240 dyn/s/cm
5; and pulmonary arterial wedge pressure or left ventricular end-diastolic pressure ≤15 mmHg. Additional requirements at entry into the study were total lung capacity ≥60 % and forced expiratory volume per second (FEV
1) ≥55 % of predicted normal values.
The key exclusion criteria were: serum alanine aminotransferase (ALT) or aspartate aminotransferase (AST) values greater than 2 times ULN, serum bilirubin value greater than 1.5 times ULN, haemoglobin concentration <10 g/dL or haematocrit <30 %, severe hypotension (diastolic blood pressure <50 mmHg or systolic blood pressure <90 mmHg), clinically significant aortic or mitral valve disease, pericardial constriction, restrictive or congestive cardiomyopathy, life-threatening cardiac arrhythmias, left ventricular ejection fraction <45 %, left ventricular outflow obstruction, symptomatic coronary artery disease, autonomic hypotension or fluid depletion, and severe hepatic and renal impairment.
Also subjects who received prohibited medications including marketed ambrisentan, bosentan, phosphodiesterase −5 inhibitor, prostanoids, intravenous inotropes, and nitric oxide were excluded from the study. The use of calcium channel blockers (CCB) and statins were permitted only if the subjects were on stable doses for at least 4 and 12 weeks, respectively, before screening. Women of childbearing potential had to use medically acceptable method of contraception (such as hormonal method, intrauterine device, barrier methods such as condom or occlusive cap) during the study; pregnant and lactating women were excluded.
The study was conducted in accordance with ICH GCP and all applicable patient privacy requirements, and, the ethical principles that are outlined in the Declaration of Helsinki. The study has received ethical approval from multiple Independent Ethnics Committees (IECs) and that the name of these can be found in Additional file
1. The protocol and protocol amendments were also approved by institutional ethics committee of each study centre. Written informed consent was obtained from subjects prior to start of the study, the names of all IECs can be found in the Additional file
1.
Assessments
The primary efficacy endpoint was the change from baseline to week 12 in the exercise capacity, as measured by the 6 min walk distance (6MWD) [
11‐
13]. Additionally, the change from baseline to week 24 in 6MWD and the changes from baseline to week 12 and 24 in NT-proBNP plasma levels, WHO FC, and BDI score were assessed as secondary endpoints [
14‐
16]. Echocardiography assessments were also performed, which included evaluation of prognostic factors such as pericardial effusion, tricuspid annular plane systolic excursion (TAPSE) and eccentricity index. Efficacy parameters (6MWD, WHO FC and BDI) were evaluated at the following time points: day 0 (predose [baseline]) and week 4, 8, 12, 16, 20 and 24 postdose. NT-pro BNP plasma levels and echocardiography parameters were assessed at baseline, week 12 and 24. Safety assessments included evaluation of time to clinical worsening of PAH, which was defined as the time from baseline to the first occurrence of death, lung transplantation, hospitalisation for PAH treatment, atrial septostomy or ambrisentan discontinuation due to change to other PAH treatment. Additionally, incidences and severity of adverse events (AEs), laboratory evaluations, liver function test, vital sign measurements, 12-lead electrocardiogram and physical examination were performed.
Statistical analysis
Assuming a dropout rate of 10 % and a study power of 80 %, a proposed sample size of 104 evaluable subjects was considered sufficient to detect a clinically and statistically significant change in 6MWD from baseline to week 12 of 23 m with a standard deviation of 83 m [
7]. Improvement in 6MWD was assessed using paired
T-test, plasma NT-proBNP levels and BDI were assessed using Wilcoxon Signed-Rank test. WHO FC and echocardiography outcomes were summarised descriptively. Last observation carry forward (LOCF) method of imputation for missing data was used for 6MWD, WHO FC and BDI evaluations. The clinical worsening events were summarised and the Kaplan-Meier analysis was performed. All the safety data was summarised descriptively. Subgroup analyses for the efficacy data was performed based on gender, subjects having PAH associated with connective tissue diseases, and subjects receiving 10 mg ambrisentan treatment.
The Intent-to-treat (ITT) population was used for analysis of efficacy and demographic/baseline characteristics. It included all subjects who received at least one dose of ambrisentan and had an efficacy assessment performed both at baseline and after administration of the ambrisentan. The safety population comprised of all subjects who received at least one dose of ambrisentan.
An adhoc analysis was performed to determine the effect of ambrisentan on heart rate recovery at 1 min (HRR1min), 2 min (HRR2 min), and 3 min (HRR3min) after exercise. HRR1min,/2 min/3 min is defined as the difference in heart rate at the end of 6MWT and at 1/2/3 min after completion of the 6MWT.