Riociguat moa
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riociguat mechanism of action soluble guanylate cyclase stimulator
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Riociguat - Mechanism of Action
Drug Class
Riociguat is the first-in-class soluble guanylate cyclase (sGC) stimulator. It is an orally administered small molecule approved for:
- Pulmonary arterial hypertension (PAH)
- Chronic thromboembolic pulmonary hypertension (CTEPH)
The NO-sGC-cGMP Pathway (Background)
In normal physiology, endothelial cells produce nitric oxide (NO), which diffuses into vascular smooth muscle cells and binds to sGC. Activated sGC converts GTP to cyclic GMP (cGMP), which activates protein kinase G (PKG), leading to smooth muscle relaxation and vasodilation.
In pulmonary hypertension, this pathway is impaired - endothelial NO synthase (eNOS) is dysfunctional, NO bioavailability is reduced, and sGC signaling is blunted, resulting in vasoconstriction and vascular remodeling.
Dual Mode of Action
Riociguat works through two complementary mechanisms:
| Mechanism | Description |
|---|---|
| 1. Direct sGC stimulation (NO-independent) | Directly stimulates sGC even in the complete absence of NO, by binding to a different site on sGC than the NO-binding heme site |
| 2. NO sensitization (NO-dependent) | Sensitizes sGC to low/residual levels of endogenous NO, amplifying the response to whatever NO is present |
Both actions converge on increased intracellular cGMP production.
Downstream Effects of Elevated cGMP
Raised cGMP activates PKG (protein kinase G), which produces:
- Pulmonary vasodilation (smooth muscle relaxation)
- Anti-proliferative effects on vascular smooth muscle cells
- Anti-fibrotic and anti-inflammatory effects on the vessel wall
- Reduced pulmonary vascular resistance (PVR)
How It Differs from PDE5 Inhibitors (e.g., Sildenafil)
Both drug classes raise cGMP, but via different mechanisms:
- PDE5 inhibitors prevent cGMP degradation (they block its breakdown enzyme)
- Riociguat increases cGMP production (it stimulates the enzyme that makes cGMP)
- Because of this, combining riociguat with PDE5 inhibitors is contraindicated - it causes severe hypotension and syncope
Pharmacokinetics (Brief)
- Excellent oral bioavailability; peak plasma concentration ~1.5 hours post-dose
- Food does not affect bioavailability
- Metabolized by CYPs 1A1, 3A, 2C8, and 2J2; major active metabolite is M1 (via CYP1A1)
- Terminal half-life ~12 hours in PAH patients (~7 hours in healthy subjects)
Key Adverse Effects
- Hypotension (especially with nitrates or PDE5 inhibitors - contraindicated combination)
- Embryo-fetal toxicity (teratogenic - contraindicated in pregnancy)
- Bleeding
- Headache, dyspepsia, dizziness, nausea, peripheral edema
Also contraindicated in: PH associated with idiopathic interstitial pneumonias (the RISE-IIP trial was terminated early due to increased mortality and serious adverse events).
Sources: Goodman & Gilman's Pharmacological Basis of Therapeutics; Fishman's Pulmonary Diseases and Disorders; Goldman-Cecil Medicine
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