Drugs That Control Pulmonary Arterial (PA) Pressure

Drugs for PAH target three core pathways in the pulmonary vasculature, all of which are deficient or overactive in PAH. A fourth, newer class (activin signal inhibitor) has recently been approved. There are currently 14 FDA-approved PAH therapies in total.

Pathways in PAH pharmacotherapy - Fuster and Hurst's The Heart, 15th Edition

1. Prostacyclin (PGI₂) Pathway

Prostacyclin is deficient in PAH. Replacing or mimicking it raises intracellular cAMP in smooth muscle cells, causing vasodilation and antiproliferation. This is the only class with proven mortality benefit (IV route).

Parenteral Prostacyclin Analogues

Drug	Route	Notes
Epoprostenol (PGI₂)	IV continuous infusion	Half-life ~6 min; requires central line; clear mortality benefit in RCTs
Treprostinil	IV or SC continuous; inhaled; oral	Half-life ~4 h; more stable; SC causes injection-site pain
Iloprost	Inhaled (6–9x/day)	Avoids IV access; pharmacological troughs between doses

Oral Prostacyclin-Class Agents

Drug	Mechanism	Notes
Selexipag	Non-prostanoid IP receptor agonist (prodrug → ACT-333679)	GRIPHON trial: reduced clinical worsening but no mortality benefit; side effects: headache, diarrhea, jaw pain
Oral treprostinil	Direct prostacyclin analogue	FREEDOM-EV trial: modest improvement when added to background therapy

Key side effects of all prostacyclin agents: flushing, headache, jaw pain, diarrhea, nausea, hypotension. Parenteral epoprostenol also reduces systemic vascular resistance by ~50%, limiting dose escalation.

2. Endothelin Receptor Antagonists (ERAs)

ET-1 is a potent vasoconstrictor and smooth muscle mitogen; it is elevated in PAH. ERAs block ET_A and/or ET_B receptors on smooth muscle to reduce vasoconstriction and vascular remodeling.

Drug	Selectivity	Key Trial	Notes
Bosentan	Non-selective (ET_A + ET_B)	BREATHE-1	First approved ERA; monthly LFT monitoring required (up to 17% get aminotransferase elevation)
Ambrisentan	Selective ET_A	ARIES-1	Less hepatotoxicity; associated with fluid retention and anemia
Macitentan	Non-selective (ET_A + ET_B), optimized binding	SERAPHIN	45% reduction in composite clinical worsening endpoint over ~85 weeks

ERAs are teratogenic (Category X). Common side effects: nasopharyngitis, fluid retention, peripheral edema, anemia. Sitaxsentan was withdrawn in 2010 due to fatal hepatotoxicity.

3. Nitric Oxide (NO) / cGMP Pathway

NO from endothelium activates soluble guanylate cyclase (sGC) → cGMP → vasodilation in smooth muscle. Two drug approaches target this:

PDE-5 Inhibitors (prevent cGMP breakdown)

Drug	Notes
Sildenafil	Oral; improves hemodynamics and 6-MWD; also used in erectile dysfunction
Tadalafil	Oral, once daily; longer half-life than sildenafil

Side effects: headache, flushing, visual disturbances, hypotension. Do NOT combine with riociguat (serious hypotension risk).

sGC Stimulator (directly stimulates sGC, NO-independent)

Drug	Notes
Riociguat	Dual mechanism: sensitizes sGC to NO AND directly stimulates sGC independent of NO. Only approved PAH drug also indicated for inoperable CTEPH (Group 4 PH). Approved 2013.

4. Activin Signal Inhibitors (Newest Class)

Drug	Mechanism	Notes
Sotatercept	Fusion protein (Fc-IgG + activin receptor II extracellular domain); traps activin ligands → rebalances TGF-β/BMPR2 pathway, reducing vascular cell proliferation	Phase 3 STELLAR trial: +40 m improvement in 6-MWD vs. placebo in patients already on background triple therapy; reduces PVR. Telangiectasia in ~10%

5. Calcium Channel Blockers (CCBs)

Used only in the minority (~10%) of patients with a positive acute vasoreactivity test (mPAP drops ≥10 mmHg to <40 mmHg with inhaled NO or adenosine during right heart catheterization).

Drug	Route
Nifedipine	Oral
Amlodipine	Oral
Diltiazem	Oral (if resting heart rate elevated)

CCBs are not used in non-responders and are contraindicated in right heart failure. They have no proven benefit in Group 2-5 PH.

6. Supportive / Adjunct Therapy

Drug	Role
Diuretics	Reduce RV preload; manage fluid retention
Anticoagulants (warfarin)	Idiopathic PAH (microvascular thrombi); use controversial
Digoxin	Adjunct in RV failure
Supplemental oxygen	Prevents hypoxic vasoconstriction (target SpO₂ >90%)

Treatment Strategy Summary

NYHA FC IV / cardiogenic shock: Start continuous IV epoprostenol (only drug with clear mortality benefit in severe PAH)
NYHA FC II-III (vasoreactivity-negative): Initial combination oral therapy is preferred - AMBITION trial showed ambrisentan + tadalafil was superior to monotherapy (18% vs. 34% vs. 28% event rate)
Escalation: Triple therapy (ERA + PDE5i + prostacyclin) is now used in high-risk patients; sotatercept can be added on top of maximal therapy
Group 2 PH (left heart disease): PAH-specific drugs are not recommended and may be harmful
CTEPH (Group 4): Riociguat is the pharmacological option; surgery (pulmonary endarterectomy) is preferred

Recent evidence note (2025-2026):

A network meta-analysis (PMID 38820258, Ann Am Thorac Soc 2024) evaluated sotatercept vs. other add-on PAH therapies, supporting its efficacy as an add-on agent
A 2026 systematic review (PMID 41678138) addressed transitioning between prostacyclin pathway agents, particularly to oral selexipag

Sources: Fuster and Hurst's The Heart 15th Ed.; Katzung's Basic and Clinical Pharmacology 16th Ed.; Harrison's Principles of Internal Medicine 22E (2025); Braunwald's Heart Disease; Harrison's Principles of Internal Medicine 22E

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