Opsumit contains the active ingredient macitentan, which is an endothelin receptor antagonist. It is available as a 10 mg film-coated tablet for oral administration. Key inactive ingredients include lactose monohydrate, magnesium stearate, and microcrystalline cellulose. Opsumit is intended to work by blocking endothelin receptors, though specific therapeutic uses are not explicitly stated in the section.

How should I use this medication?

Take this medication by mouth. Take it as directed on the prescription label at the same time every day. Do not cut, crush, or chew this medication. Swallow the tablets whole. You can take it with or without food. If it upsets your stomach, take it with food. Keep taking it unless your care team tells you to stop.

A special MedGuide will be given to you by the pharmacist with each prescription and refill. Be sure to read this information carefully each time.

Talk to your care team about the use of this medication in children. Special care may be needed.

Overdosage: If you think you have taken too much of this medicine contact a poison control center or emergency room at once.

NOTE: This medicine is only for you. Do not share this medicine with others.

What if I miss a dose?

If you miss a dose, take it as soon as you can. If it is almost time for your next dose, take only that dose. Do not take double or extra doses.

Where should I keep my medication?

Keep out of the reach of children and pets.

Store at room temperature between 20 and 25 degrees C (68 and 77 degrees F). Get rid of any unused medication after the expiration date.

To get rid of medications that are no longer needed or have expired:

• Take the medication to a medication take-back program. Check with your pharmacy or law enforcement to find a location.
• If you cannot return the medication, check the label or package insert to see if the medication should be thrown out in the garbage or flushed down the toilet. If you are not sure, ask your care team. If it is safe to put it in the trash, empty the medication out of the container. Mix the medication with cat litter, dirt, coffee grounds, or other unwanted substance. Seal the mixture in a bag or container. Put it in the trash.

NOTE: This sheet is a summary. It may not cover all possible information. If you have questions about this medicine, talk to your doctor, pharmacist, or health care provider.

What side effects may I notice from receiving this medication?

Side effects that you should report to your care team as soon as possible:

• Allergic reactions—skin rash, itching, hives, swelling of the face, lips, tongue, or throat
• Liver injury—right upper belly pain, loss of appetite, nausea, light-colored stool, dark yellow or brown urine, yellowing skin or eyes, unusual weakness or fatigue
• Low red blood cell level—unusual weakness or fatigue, dizziness, headache, trouble breathing

Side effects that usually do not require medical attention (report to your care team if they continue or are bothersome):

• Headache
• Runny or stuffy nose
• Sore throat
• Swelling of the ankles, hands, or feet

This list may not describe all possible side effects. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

What should I tell my care team before I take this medication?

They need to know if you have any of these conditions:

• Liver disease
• Low red blood cell levels
• An unusual or allergic reaction to macitentan, other medications, foods, dyes, or preservatives
• Pregnant or trying to get pregnant
• Breastfeeding

What may interact with this medication?

Do not take this medication with any of the following:

• Sparsentan

This medication may also interact with the following:

• Amiodarone
• Antiviral medications for HIV or hepatitis
• Certain medications for fungal infections, such as fluconazole, ketoconazole, itraconazole, posaconazole
• Rifampin

Other medications may affect the way this medication works. Talk with your care team about all of the medications you take. They may suggest changes to your treatment plan to lower the risk of side effects and to make sure your medications work as intended.

This list may not describe all possible interactions. Give your health care provider a list of all the medicines, herbs, non-prescription drugs, or dietary supplements you use. Also tell them if you smoke, drink alcohol, or use illegal drugs. Some items may interact with your medicine.

What should I watch for while using this medication?

Visit your care team for regular checks on your progress. Tell your care team if your symptoms do not start to get better or if they get worse.

You may need blood work done while you are taking this medication.

Talk to your care team if you may be pregnant. Serious birth defects can occur if you take this medication during pregnancy and for 1 month after the last dose. You will need a negative pregnancy test before starting this medication. Contraception is recommended while taking this medication and for 1 month after the last dose. Your care team can help you find the option that works for you.

Talk to your care team before breastfeeding. Changes to your treatment plan may be needed.

This medication may cause infertility. Talk to your care team if you are concerned about your fertility.

What are the most serious risks of this medication?

Do not take this medication if you may be pregnant. Serious fetal side effects may occur.