Study of Add-on Ambrisentan Therapy to Background Phosphodiesterase Type-5 Inhibitor (PDE5i) Therapy in Pulmonary Arterial Hypertension (ATHENA-1)

To evaluate the change from baseline in pulmonary vascular resistance (PVR), and other hemodynamic parameters, following the addition of ambrisentan to background phosphodiesterase type-5 inhibitor (PDE-5i) therapy in subjects with pulmonary arterial hypertension (PAH) who have demonstrated a sub-optimal response to PDE-5i monotherapy.

The study was originally designed as a 2-arm, double-blind, randomized study in which patients received ambrisentan or placebo for 24 weeks, and then received ambrisentan blinded to dose for 24 weeks. With Protocol Amendment 2 (12 June, 2009), the study was switched to single-arm, open-label treatment, and all patients remaining in the placebo arm were switched to open-label ambrisentan treatment. Patients who enrolled after Amendment 2 all received open-label ambrisentan.

The primary objective of this study is to evaluate the change from baseline in pulmonary vascular resistance (PVR), and other hemodynamic parameters, following the addition of ambrisentan to background phosphodiesterase type-5 inhibitor (PDE-5i) therapy in subjects with pulmonary arterial hypertension (PAH) who have demonstrated a sub-optimal response to PDE-5i monotherapy.

The secondary objectives of this study are to evaluate the change from baseline in other clinical measures of PAH following the addition of ambrisentan to background PDE-5i therapy in subjects with PAH who have demonstrated a sub-optimal response to PDE-5i monotherapy.

The safety and tolerability of ambrisentan/PDE-5i combination therapy will be evaluated throughout the study. In addition, long-term efficacy will be examined.

Eligibility Criteria:
Selected Inclusion Criteria

* Must be between 16 and 75 years of age;
* Must weigh at least 40 kg;
* Have a current diagnosis of idiopathic PAH, familial PAH, or PAH that is primarily due to connective tissue disease, congenital heart defects, drug or toxin use, or human immunodeficiency virus (HIV);
* Have WHO functional class III symptoms;
* Be receiving sildenafil or tadalafil monotherapy for the treatment of PAH for at least the past 12 weeks and at a stable dose for at least 8 consecutive weeks;
* Meet all of the following hemodynamic criteria by means of a right heart catheterization: mPAP of at least 25 mmHg; PVR of at least 400 dyne\*sec/cm5; pulmonary capillary wedge pressure (PCWP) or left ventricular end diastolic pressure (LVEDP) of not more than 15 mmHg;
* Meet all of the following pulmonary function test criteria no more than 12 weeks before the screening visit: total lung capacity at least 60% of predicted normal and forced expiratory volume in 1 second of at least 65% of predicted normal;
* Able to walk at least 150 meters during the screening 6-minute walk test (6MWT);
* If receiving calcium channel blockers or 5-hydroxy-3-methylglutaryl-coenzyme A reductase inhibitors (i.e., statins) must be on stable therapy for at least 4 weeks;
* If diagnosed with HIV, must have stable disease status.

Selected Exclusion Criteria:

* Have a current pulmonary hypertension diagnosis other than idiopathic PAH, familial PAH, or PAH that is primarily due to connective tissue disease, congenital heart defects, drug or toxin use, or HIV;
* Have left ventricular ejection fraction (LVEF) ≤40% or clinically significant ischemic, valvular, or constrictive heart disease;
* Have received chronic prostanoid or endothelin receptor antagonist (ERA) therapy (eg, bosentan, sitaxsentan) within the past 12 weeks;
* Have discontinued ERA treatment for any adverse reaction other than those associated with liver function test abnormalities;
* Have received IV inotropes within 2 weeks;
* Have a serum alanine aminotransferase (ALT) or aspartate aminotransferase (AST) value that is greater than 2.0x the upper limit of normal.