Common side effects:

• Headache
• Irritation of the airways and nasal passages 
• Flu-like symptoms
• Fluid retention 
• Urinary tract infection

Seek medical attention immediately if you develop:

• Symptoms of worsening PAH, including: difficulty breathing, fluid retention or weight gain, and/or dizziness or passing out
• An allergic reaction, including: swelling of the mouth, tongue, face, and throat; itching; rash; and/or difficulty breathing

Macitentan is an endothelin receptor antagonist (ERA) that lowers blood pressure in the lungs, making it easier for the heart to pump more efficiently. Macitentan helps prevent blood vessels from narrowing by blocking endothelin, a protein that causes blood vessels in the lungs to narrow.  This may help to slow pulmonary arterial hypertension (PAH) progression and decrease symptoms.

Do not take macitentan if you:

• Are allergic to macitentan 
• Are pregnant or breastfeeding
• Have severe liver disease

Drug Interactions: These medications MAY interact with macitentan

• rifampin 
• some medications used to treat fungal infections e.g. ketoconazole and voriconazole 
• some medications used to treat HIV infection e.g. darunavir, ritonavir, and nelfinavir 
• some medications for seizure disorders e.g. phenytoin and carbamazepine 

Use in pregnancy: Macitentan can cause serious birth defects if taken during pregnancy. Females who are able to get pregnant must take a pregnancy test before starting macitentan. Monthly pregnancy tests during treatment are recommended to allow the early detection of pregnancy. Reliable forms of contraception must be used when on macitentan.

Use in breastfeeding: It is not known if macitentan can pass into breast milk. Therefore, breastfeeding is not recommended.