Opsumit (macitentan) is a medicine used to treat pulmonary arterial hypertension (PAH). PAH is a serious condition where the blood pressure in the arteries supplying the lungs is abnormally high, causing the right side of the heart to work harder and eventually leading to heart failure.

Macitentan is an endothelin receptor antagonist (ERA). It works by blocking endothelin-1, a substance that causes blood vessels in the lungs to tighten and narrow. By blocking this effect, Opsumit relaxes and widens the pulmonary blood vessels, reducing the pressure on the heart.

Opsumit is usually used in combination with other PAH medicines such as sildenafil or tadalafil.

Take one 10 mg tablet once daily, with or without food, at the same time each day.

Swallow the tablet whole. Do not crush or split it.

Do not stop taking Opsumit without speaking to your PAH specialist. PAH is a progressive disease and stopping treatment can cause rapid deterioration.

Take the missed dose as soon as you remember. If it is nearly time for your next dose, skip the missed dose and continue your normal schedule. Never take two doses in one day.

Contact your doctor or emergency department. There is no specific antidote, but supportive care can be provided.

• Store below 30°C
• Keep in the original packaging
• Keep out of reach of children

Common side effects:

• Anaemia (low red blood cells): Opsumit commonly reduces haemoglobin. Blood tests are required before and during treatment
• Headache
• Respiratory infections
• Nausea
  
  

Serious side effects:

• Liver toxicity: liver function must be monitored. Report symptoms such as jaundice (yellowing of skin or eyes), dark urine, or unusual fatigue
• Fetal harm: macitentan causes severe birth defects and must not be taken during pregnancy. Women of childbearing age must use two reliable forms of contraception during treatment and for one month after stopping

Due to the risk of fetal harm, Opsumit is only available through a controlled distribution programme.

• Strong CYP3A4 inducers (rifampicin, carbamazepine, St John's Wort): reduce macitentan levels. Avoid
• Strong CYP3A4 inhibitors (ketoconazole, ritonavir): increase macitentan levels

Tell your PAH specialist and pharmacist about all medicines you take.

Why is contraception so important with Opsumit?

Macitentan, like other endothelin receptor antagonists, is known to cause serious birth defects if taken during pregnancy. It can affect fetal blood vessel development and cause life-threatening complications. For this reason, all endothelin receptor antagonists including Opsumit are only dispensed through controlled distribution programmes that include pregnancy prevention measures. If you are a woman who could become pregnant, two reliable methods of contraception are required throughout treatment and for one month after stopping.

Can Opsumit be used with other PAH medicines?

Yes. Opsumit is often combined with PDE5 inhibitors such as sildenafil (Revatio) or tadalafil as part of a combination PAH treatment strategy. Clinical trials have shown that combination therapy with macitentan reduces the risk of disease progression more than either drug alone.

Ace provides accurate and independent information medically reviewed on prescription medications. This material is provided for educational purposes only and is not intended for medical advice, diagnosis or treatment.