Sotatercept: A New Treatment Paradigm for Pulmonary Arterial Hypertension

After the first trimester, amlodipine and other calcium channel blockers are reasonably safe. For eclampsia or hypertension specifically during pregnancy, the preferred agent is a direct alpha agonist, such as prazosin.

Any mean pulmonary artery pressure greater than 20 mmHg combined with a pulmonary vascular resistance greater than 2 Wood units should be started on therapy — at minimum, a PDE5 inhibitor plus an endothelin receptor antagonist as double therapy. If the patient remains symptomatic, we add a prostacyclin analog to complete triple therapy. Escalating beyond triple therapy to sotatercept should only be considered after at least six months to a year of adequate triple therapy without sufficient response.

First, PDE5 inhibition, to promote vascular relaxation via the cGMP pathway. Second, soluble guanylate cyclase stimulation, to address back-pressure and encourage vasodilation. Third, endothelin receptor blockade, to retard smooth muscle cell hypertrophy and reduce pulmonary vascular resistance. Sotatercept adds a fourth, distinct pathway — anti-proliferative inhibition of activin signalling — which addresses the underlying vascular remodelling rather than just haemodynamics.

The right ventricle is a volume-handling ventricle, not designed for pressure overload — you can load it with considerable volume and it won't fail, because volume is its domain. But impose a pressure overload, as in pulmonary hypertension, and it hypertrophies to compensate before eventually failing. The left ventricle is a pressure-handling ventricle, built for exactly that load. That's why pulmonary hypertension causes right heart failure long before it affects the left.

Two mechanisms operate together. Viral proteins cause stiffness in the lung's interstitial tissue, which physically compresses the pulmonary blood vessels. At the same time, the immunocompromised state associated with HIV promotes smooth muscle hyperplasia within the vessel walls, narrowing the lumen from within. It's the combination of external compression and internal luminal narrowing that drives HIV-associated pulmonary hypertension.

Unlike earlier therapies, which all work by vasodilation, sotatercept is an activin signalling inhibitor that prevents smooth muscle cell proliferation in the pulmonary vasculature, directly targeting the structural vascular disease rather than just its haemodynamic consequences.

In the STELLAR trial, patients with idiopathic, hereditary, or persistent pulmonary arterial hypertension of the newborn who received sotatercept on top of background therapy showed a 38 to 40 percent improvement in symptoms, and over 40 percent did not progress to needing a lung transplant or prolonged hospitalisation.

Sotatercept is given as a subcutaneous injection once every three weeks, at a cost of approximately 10,000 US dollars per vial.

Known risks include stroke and thrombotic events, meaning patients need to be selected and monitored carefully.

Sotatercept is not a first-line treatment; it is considered for patients with Group 1 disease who have completed an adequate trial of triple combination therapy, typically six months to a year, without sufficient response.