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If you are living with pulmonary arterial hypertension (PAH), you may be prescribed bosentan (Tracleer). Bosentan, which has been around for over 20 years, was the first endothelin receptor antagonist (ERA) approved for PAH.

Bosentan works by blocking the effects of a substance that causes blood vessels to narrow, allowing them to relax and widen. This can improve your ability to exercise and slow the progression of PAH. But along with these benefits, bosentan can also cause side effects - from headaches to swelling. Here's what you should know about bosentan side effects.

Bosentan side effects at a glance

Most bosentan side effects are mild and can be managed at home. But some are serious and require special monitoring or medical attention. Here are the bosentan side effects that were reported during initial clinical trials.

Common bosentan side effects (reported by at least 3% of people taking it) include:

• Respiratory tract infection

• Fainting

• Headache

• Flushing

• Low blood pressure

• Sinusitis (inflamed nose passages)

• Chest pain

• Joint and muscle ache

• Irregular heartbeat

• Anemia (low red blood cell count)

• Swelling

• Elevated liver enzymes

Other potential bosentan side effects include:

• Decreased sperm counts

• Rash

• Low platelet (blood-clotting cell) counts

Boxed warnings for bosentan include:

• Liver damage

• Harm to a growing fetus

Below, we cover 10 bosentan side effects, how to manage them, and when to contact your care team.

1. Respiratory tract infection

During clinical trials, respiratory tract infections (RTIs) were the most commonly reported bosentan side effect. But it's not clear if bosentan itself increases the risk of RTIs. Even so, RTIs can be serious if you have PAH. They can worsen PAH symptoms and lead to complications, such as pneumonia.

If you feel like you're coming down with a cold or other respiratory illness while taking bosentan, tell your healthcare team. Depending on your symptoms, they may want to do further testing to figure out the cause. In some cases, treatments may be available to help you get better faster or lower the risk of complications.

Your healthcare team can also suggest over-the-counter (OTC) remedies to help manage your symptoms. Steer clear of products that contain decongestants, such as Sudafed (pseudoephedrine), since they can worsen PAH symptoms. It's also a good idea to avoid nonsteroidal anti-inflammatory drugs, such as ibuprofen (Advil, Motrin).

2. Headache

Headache is another commonly reported bosentan side effect. But it's important to note that bosentan is often prescribed with other medications that can cause headaches, such as sildenafil (Revatio) and tadalafil (Adcirca).

If you experience a mild headache while taking bosentan, you may be able to try an OTC pain reliever for relief, such as acetaminophen (Tylenol). Lack of sleep can worsen headaches, so try to get enough sleep each night (7 to 9 hours). And follow your prescriber's instructions regarding how much fluid you drink every day.

Your headaches may resolve as your body gets used to the medication. But contact your care team right away if they feel severe or if they're getting worse.

3. Swelling

Fluid retention is possible while taking bosentan. You may notice swelling in your legs or your hands and some weight gain as a result. These are common side effects of ERAs, but the risk of swelling may vary between medications.

Fluid retention is common in people with PAH, with or without bosentan. This is especially the case for people who've developed heart failure, which can happen as PAH progresses. Excess fluid can worsen heart failure and PAH symptoms, so it should be addressed right away.

Tell your prescriber if you notice swelling or changes in your body weight after starting bosentan. They may prescribe a diuretic (water pill) to help remove the excess fluid and give you instructions for how to manage your sodium (salt) and fluid intake. In some cases, they may switch you to a medication with a lower risk of swelling.

4. Chest pain and heart palpitations

During clinical trials, some people taking bosentan reported chest pain and heart palpitations as side effects. But it's important to note that both are common PAH symptoms. So they may not necessarily be from bosentan.

Even so, chest pain and heart palpitations can be a sign of something more serious. If your chest pain is accompanied by symptoms such as shortness of breath, seek emergency medical care. This is also the case if you're experiencing heart palpitations that last more than a few minutes. Pain in the neck or jaw and feeling as if you're going to pass out are also symptoms that warrant medical attention.

5. Low blood pressure

Bosentan causes your blood vessels to widen, which can lower your blood pressure. In some cases, it's possible for your blood pressure to drop too low (hypotension). This risk may be higher if you're taking it with other medications that also lower your blood pressure.

Drops in blood pressure can make you feel dizzy or lightheaded. So it's a good idea to avoid doing any activity in which dizziness can be risky until you know how bosentan affects you. Try to change positions, such as going from lying down to standing, more slowly to avoid falls.

Over time, your body may adjust to blood pressure changes from bosentan. But it's still important to tell your prescriber if you're experiencing symptoms. They may need to adjust your medication regimen if your blood pressure is dropping too low.

Get emergency medical attention if you feel as if you're going to faint. Your blood pressure may be dangerously low.

6. Joint pain

Joint pain is possible while taking bosentan. But it's important to note that most people with PAH experience musculoskeletal pain (pain affecting bone, muscle, or joints). It's possible that bosentan could make this type of pain more likely.

If you notice joint pain starting or getting worse after taking bosentan, tell your prescriber.

Depending on the severity, they can recommend OTC or prescription pain relievers, including topical creams and gels. They can also recommend safe exercises to improve your joint mobility. At home, you can also try ice and heat therapy for some relief.

7. Liver damage

Bosentan has a boxed warning (a serious warning given to medications) about the risk of liver damage. Because of this, you'll be enrolled in a mandatory risk management program that requires regular monitoring of your liver health.

Bosentan can elevate liver enzymes, which can be a sign of liver inflammation or damage. This doesn't usually cause noticeable symptoms, and it can often be managed by lowering your dose. But in rare cases, more serious liver damage is possible.

Before starting bosentan, your healthcare team will order liver tests to make sure it's OK for you to take the medication. They'll repeat these tests every month, adjusting your dose as needed. Tell them right away if you develop symptoms such as nausea and vomiting, abdominal pain, or yellowing of the skin or eyes (jaundice).

8. Harm to a growing fetus

Bosentan also has a boxed warning that it can harm a growing fetus if taken during pregnancy. Because of this, you'll need to meet additional requirements while taking bosentan if you're able to get pregnant.

As part of the mandatory risk management program, a negative pregnancy test is required before starting bosentan. After that, you'll need to take a pregnancy test every month during treatment and 1 month after stopping bosentan. You'll also need to use two reliable forms of birth control or an intrauterine device (IUD) during this time or have had tubal surgery to prevent future pregnancy.

Ask your care team about recommended birth control options for your situation. They can tell you which combinations are adequate with bosentan, which can interact with many hormonal forms of birth control. Tell them right away if you think you might be pregnant while taking bosentan. They can help you figure out your next steps.

9. Reduced sperm count

Although uncommon, reduced sperm counts have been reported in some men taking bosentan, as well as other ERAs. But in most cases, this side effect appears to be temporary.

If you and your partner are planning to get pregnant, talk to your care team before starting bosentan. They can help you determine what steps you can take to increase your chance of success.

10. Anemia

People taking bosentan can experience a mild decrease in their red blood cell count within weeks of starting the medication. Your care team will most likely check your blood count at 1 and 3 months after starting bosentan.

After that, the manufacturer recommends checking the blood count every 3 months. This helps make sure you don't develop anemia - when your red blood cell count is too low. Taking a higher dose of bosentan increases the risk of having this side effect.

Talk to your care team if you experience symptoms of anemia, such as fatigue, pale skin, or brittle nails. They can recommend the next steps.

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