Macitentan, manufactured and marketed by San Francisco-based Actelion Pharmaceuticals under the trade name Opsumit, is a novel, oral formulation aimed at treating patients with pulmonary arterial hypertension (PAH). Chemically known as N-[5-(4-Bromophenyl)-6-[2-[(5-bromo-2-pyrimidinyl)oxy]ethoxy]-4-pyrimidinyl]-N’-propylsulfamide, macitentan is an endothelin receptor antagonist (ERA) which ensures vasodilation amidst the constricted blood vessels in the pulmonary arterial endothelium and restores normal blood flow through the pulmonary artery.
How Opsumit (Macitentan) Works
Macitentan is a dual ERA, which acts against binding of the endothelin protein to its receptors. Endothelin receptors are evenly distributed on the surface of the arterial smooth muscles and are specific to endothelin-1 (ET-1 is the most common form of the protein) secreted by the endothelial cells. These receptors are also G protein coupled receptors. Upon secretion, these receptors get activated and cause an increase in the calcium levels in blood, which in turn causes vasoconstriction. This paves the way for the development of PAH. Macitentan has the potential to block these receptors, being more specific for endothelin receptor A (ETA is chiefly responsible for vasoconstriction) and causes dilation of blood vessels.
Opsumit (Macitentan) Clinical Trials
Opsumit was approved by the U.S. FDA in October 2013. The announcement came after Actelion released data for its landmark clinical trial trial SERAPHIN, which recruited a study population of 742 patients, the only trial to have run for two years and focused on morbidity and mortality as its end-points instead of just a reduction in pulmonary arterial pressures.
Patients were given doses of Opsumit (3 mg and 10 mg once daily) against that of a placebo. Opsumit proved effective when both administered as a monotherapy or in combination with other non-PAH medications which did not affect the former’s effects. The reduction in clinical deterioration and improvement in exercise abilities were monitored via the 6 minute walk distance (6MWD) tests.
Opsumit (Macitentan) Dosing
The drug is available in orally consumed tablets, 10 mg in strength. It is normally prescribed once daily until otherwise stated. Female patients can receive the drug only through the Opsumit Risk Evaluation and Mitigation Strategy (REMS) Program, and pregnant women are strictly advised against taking the drug due to potential damage to the developing fetus. Commonly noted adverse effects include low red blood cell count (anemia), nasopharyngitis, sore throat, bronchitis, headache, flu, and urinary tract infection. Peripheral edema might also be another severe adverse effect which would need immediate medical attention.
Patients are advised not to take the drug if they are also taking mifepristone, nefazodone, St. John’s wort, or medicines usually taken for cancer, hepatitis C, HIV, infections, or seizures.
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