Pulmonary Arterial Hypertension: New Combination Treatments and Who Qualifies for Them

Research-informed explainer — last updated April 12, 2026

Pulmonary arterial hypertension is a severe, progressive disease driven by abnormal proliferation of pulmonary vascular cells — and the shift from sequential monotherapy to upfront combination therapy has changed survival trajectories for patients who qualify. Understanding the three biological pathways targeted by PAH drugs, and which patient characteristics predict benefit from aggressive initial treatment, is central to informed decision-making.

This article draws on research from Serpil Erzurum, MD, at Cleveland Clinic, who has authored landmark papers on PAH pathobiology including the hyperproliferative endothelial cell studies; Roham Zamanian, MD, Professor of Pulmonary Vascular Medicine at Stanford, who characterized connective tissue disease-associated PAH and the role of insulin resistance; Andrew Shorr, MD, Professor of Medicine at Georgetown University and MedStar Washington Hospital Center, who quantified the prevalence and outcomes of PAH complicating pulmonary fibrosis; Noah Lechtzin, MD, Associate Professor at Johns Hopkins, who co-authored the ambrisentan plus tadalafil combination trial in scleroderma-associated PAH; and Raed Dweik, MD, at Cleveland Clinic, who published extensively on portopulmonary hypertension.

What Is Pulmonary Arterial Hypertension?

PAH (WHO Group 1 pulmonary hypertension) is characterized by progressive obstruction and remodeling of the small pulmonary arteries, leading to rising right heart afterload, right ventricular failure, and death. It is distinct from pulmonary hypertension caused by left heart disease (Group 2), hypoxic lung disease (Group 3), or chronic thromboembolic disease (Group 4) — and treatments developed for PAH Group 1 are not appropriate for other groups.

Dr. Erzurum's pathobiology review (cited 568 times) details the cellular hallmarks: endothelial cells in PAH lungs become hyperproliferative and resistant to apoptosis, forming plexiform lesions that obliterate the vascular lumen. Her earlier mechanistic paper (cited 384 times) showed that idiopathic PAH endothelial cells behave more like tumor cells than normal vascular endothelium — proliferating autonomously and escaping programmed cell death signals. This biology explains why PAH requires targeted molecular therapy rather than vasodilators alone.

Dr. Erzurum's Nature Medicine paper (cited 355 times) identified a disrupted apelin-FGF signaling axis in PAH, opening lines of investigation into new molecular targets that may eventually expand the therapeutic armamentarium.

The Three Therapeutic Pathways

PAH therapy targets three distinct molecular pathways:

Endothelin receptor antagonists (ERAs) — Ambrisentan and macitentan block endothelin-1 receptors on pulmonary vascular smooth muscle, reducing vasoconstriction and vascular remodeling. Bosentan was the original ERA and remains used in some settings.

PDE5 inhibitors and sGC stimulators — Sildenafil, tadalafil, and riociguat act through the nitric oxide-cGMP pathway, promoting vasodilation and inhibiting smooth muscle proliferation. Tadalafil is preferred in combination therapy for its once-daily dosing and drug-drug interaction profile.

Prostacyclin pathway agonists — Epoprostenol (continuous IV infusion), treprostinil (IV, subcutaneous, or inhaled), and selexipag (oral) activate prostacyclin receptors to promote vasodilation and inhibit platelet aggregation and smooth muscle proliferation. Prostanoid therapy is typically reserved for higher-risk patients due to complexity of administration.

The Case for Upfront Combination Therapy

The AMBITION trial — one of the most influential PAH trials of the past decade — compared upfront combination therapy with ambrisentan plus tadalafil against either drug alone in treatment-naive patients. The combination arm reduced the composite endpoint of death, hospitalization for worsening PAH, or disease progression by 50% compared to ERA or PDE5 inhibitor monotherapy. The benefit was driven primarily by fewer first hospitalizations and fewer treatment failure events.

Dr. Lechtzin and colleagues contributed to the trial in scleroderma-associated PAH examining ambrisentan and tadalafil up-front combination (cited 164 times), confirming that this connective tissue disease subgroup derives benefit from the same approach. This was important because scleroderma-PAH has traditionally been considered more refractory and carries a worse prognosis than idiopathic PAH.

Which Patients Qualify — and the Crucial Subgroup Question

Dr. Zamanian's REVEAL registry characterization of connective tissue disease-associated PAH (cited 428 times) showed that this subgroup — particularly systemic sclerosis — had the worst 1-year survival of all PAH subtypes: approximately 82% vs. 92% for idiopathic PAH. Understanding the underlying etiology matters enormously for prognosis and for treatment sequencing.

Dr. Zamanian's insulin resistance paper (cited 273 times) found that PAH patients have a high prevalence of insulin resistance independent of obesity, associated with worse hemodynamics and exercise capacity. This metabolic phenotype may eventually guide metabolic co-targeting strategies.

Risk stratification using validated tools — including the REVEAL calculator, ERS/ESC 4-strata risk model, and 6-minute walk distance — is used to determine initial therapy intensity. Low-risk patients (good exercise tolerance, no right heart failure signs, favorable hemodynamics) may begin with dual oral therapy. High-risk patients (rapidly progressive, severely reduced 6MWD, right heart failure) are candidates for triple therapy including upfront IV or subcutaneous prostanoids.

PAH Complicating Other Lung Diseases

Dr. Shorr's CHEST Journal paper (cited 866 times) documented that PAH complicates up to 32% of advanced IPF cases awaiting lung transplant, and that its presence dramatically worsens transplant outcomes. A subsequent European Respiratory Journal paper (cited 368 times) in a transplant-listed IPF cohort confirmed that PAH was the strongest predictor of waitlist mortality.

This population — Group 3 pulmonary hypertension in the context of lung disease — is clinically distinct from Group 1 PAH. Most PAH-specific drugs have not shown benefit and some may worsen outcomes by causing ventilation-perfusion mismatch. The exception is inhaled treprostinil, which received FDA approval in 2021 for PAH associated with interstitial lung disease based on the INCREASE trial.

Portopulmonary Hypertension: A Separate Subtype

Dr. Dweik's CHEST Journal paper on portopulmonary hypertension (cited 283 times) detailed this distinct PAH subtype occurring in patients with portal hypertension — most commonly cirrhosis. PoPH is found in approximately 5-8% of patients evaluated for liver transplantation. The mechanism involves portal hypertension driving increased pulmonary blood flow and vasoactive mediator release. Importantly, PAH-specific therapies (ERAs, PDE5 inhibitors, and prostanoids) can reduce pulmonary pressures enough to allow liver transplantation in carefully selected patients. Untreated severe PoPH is a contraindication to transplantation.

Questions to ask your doctor

• What WHO group is my pulmonary hypertension, and does that affect which drugs are appropriate for me?
• Based on my REVEAL score or ESC/ERS risk category, should I start on combination therapy from day one?
• Have I had right heart catheterization, and if not, when should I have it to confirm the diagnosis and measure hemodynamics?
• If I have connective tissue disease or liver disease, how does my underlying condition affect my treatment options?
• Is my disease progressing despite current therapy, and if so, what is the next escalation step?

The bottom line

PAH is a biologically complex disease of the pulmonary vasculature, driven by endothelial hyperproliferation and three distinct molecular pathways — each targetable by approved drugs. Upfront combination therapy with an ERA and PDE5 inhibitor reduces clinical failure events by 50% compared to monotherapy in treatment-naive patients, and is now the standard of care for low-to-intermediate risk patients. The etiology of PAH matters — portopulmonary, connective tissue disease-associated, and fibrosis-related subtypes each have different prognoses, different treatment considerations, and different transplant implications that require evaluation by a PAH specialist.