Welireg (belzutifan) is a prescription medicine used to treat certain cancers. It may help slow the growth and spread of cancers in some people.
Like most cancer treatments, Welireg can cause side effects and may interact with other medicines. Some side effects are mild, while others can become serious and require close monitoring or changes to your treatment plan.
Keep reading to learn about possible Welireg side effects, how they may be managed, and which interactions are important to know about.
This article does not include every possible side effect or interaction. Tell your health care provider about any new or worsening symptoms while taking Welireg.
Welireg Side Effects
While the side effects of Welireg can vary depending on the condition being treated, common side effects may include:
- Low red blood cell counts (anemia), among other changes in blood test results
- Tiredness (fatigue)
- High blood pressure
- Muscle or joint pain
- Diarrhea
- Headache
- Shortness of breath
- Low thyroid hormone levels (hypothyroidism)
- Rash
- Dizziness
- Nausea or vomiting
- Constipation
- Swelling from fluid retention (edema)
While less common, potentially serious side effects of Welireg may include:
- Severe anemia
- Low oxygen levels (hypoxia)
- Heart problems, such as heart failure
- Serious allergic reactions, including trouble breathing, hives, or throat swelling
If you have symptoms that feel serious or life-threatening, seek medical care right away.
How to Manage Welireg Side Effects
Some Welireg side effects can be managed with simple strategies or by closely monitoring symptoms and lab tests. Welireg can cause anemia and low oxygen levels, and these side effects sometimes result in the need to pause treatment, adjust the dose, or stop treatment. So, it is important to identify symptoms early and stay in close contact with your health care provider.
Keep in mind that you should not stop or change your treatment plan without first discussing it with your health care team. The sections below include some of the possible side effects of Welireg and possible ways to manage them. Tell your health care provider if these side effects bother you or do not go away.
Anemia
Anemia, or low red blood cell counts, is the most common side effect of Welireg. In studies, anemia affected up to 96% of people taking Welireg.
Symptoms of anemia may include:
- Tiredness
- Feeling cold
- Shortness of breath
- Fast heartbeat
- Chest pain
Your health care provider will check your red blood cell levels before you start treatment and throughout treatment with Welireg. Welireg can cause severe anemia that may require blood transfusions.
To help catch anemia early, keep all appointments for blood tests while taking this medicine. Your health care provider may also prescribe treatment or recommend over-the-counter (OTC) supplements to help manage anemia. This side effect can usually be managed, but some people may need to pause or stop treatment under the guidance of a health care provider.
Low oxygen levels
Welireg can cause low oxygen levels in the body (hypoxia). In studies, some people had hypoxia that required oxygen therapy, hospitalization, dose changes, or stopping treatment.
Low oxygen levels mean your body is having trouble getting the oxygen it needs, which may lead to symptoms such as shortness of breath, cough, or wheezing. Other symptoms of low oxygen levels may include:
- Fast heartbeat
- Changes in the color of your skin or lips
- Confusion
Your health care team will check your oxygen levels before and during treatment with Welireg. Avoid smoking or other activities that may worsen your breathing problems.
If Welireg causes low oxygen levels while you are resting, your health care provider may temporarily stop the medicine until your oxygen levels improve. Depending on how severe the problem is, they may restart Welireg at a lower dose or stop treatment permanently.
Heart problems
When Welireg is taken together with another medicine called lenvatinib, it can cause serious heart problems, including heart failure. In studies, serious heart problems occurred in about 6% of people taking Welireg with lenvatinib.
Symptoms of heart problems may include:
- Shortness of breath
- Swelling of your ankles
- Unusual weight gain
- Chest pain
- Feeling faint
Before starting Welireg with lenvatinib, your health care provider may do tests to see how well your heart is pumping. Keep all appointments with your health care provider for heart check-ups. Tell your health care provider right away if you have any signs or symptoms of heart problems.
If heart problems occur, your health care provider may pause treatment, reduce your dose, or stop Welireg and lenvatinib permanently depending on how serious the problem is. Welireg in combination with lenvatinib has not been studied in people whose heart is not working as well as it should.
Tiredness
Welireg may cause tiredness or low energy (fatigue). Tiredness is a common side effect of many cancer treatments and may be a symptom of the cancer itself.
To help boost your energy and manage fatigue, try the following:
- Get plenty of sleep and maintain a regular sleep schedule.
- Eat a balanced diet with enough calories and nutrient-rich foods to support your body.
- Stay active with light exercise, such as walking or stretching, as part of your daily routine, if possible.
- Some people may feel energized by connecting with others. Reach out to friends or family, or consider participating in a support group.
- Plan important tasks when you have the most energy.
Tell your health care provider if your fatigue feels too hard to manage. If needed, your health care provider may adjust your dose or pause your Welireg treatment.
Headache
Headache is a commonly reported side effect of Welireg. Symptoms may include head pain or pressure.
To help manage headaches:
- Rest in a quiet, dark room if needed.
- Drink enough fluids throughout the day.
- Try relaxation techniques, such as deep breathing.
An OTC pain reliever may help ease headache pain, but check with your health care provider or pharmacist first to make sure it is safe for you.
Nausea
Nausea is another common side effect of Welireg. In studies, some people had severe nausea that resulted in their health care provider adjusting their dose or pausing or stopping the medicine.
Strategies to help manage nausea:
- Eat small, frequent meals and sip on cool, clear liquids slowly throughout the day.
- Choose bland foods that are gentle on the stomach, such as crackers, toast, or broth.
- Try ginger chews, sour candies, or mints to help with queasiness.
Tell your health care provider if nausea feels severe or doesn’t go away. If needed, your health care provider may prescribe anti-nausea medicines, or they may adjust or pause your Welireg treatment.
Welireg Interactions to Know About
Welireg can interact with certain medicines. Some drug interactions may increase the risk of side effects from Welireg, while other interactions may make certain medicines not work as well.
This is not a full list of interactions. Tell your health care provider and pharmacist about all prescription and OTC medicines, vitamins, and supplements you use before starting Welireg.
Medicines that can increase Welireg side effects
Some medicines can affect how well the body breaks down Welireg. This can raise Welireg levels in the body and increase the risk of side effects, including anemia or low oxygen levels.
A few examples are:
- Fluconazole
- Fluvoxamine
- Gemfibrozil
Your health care provider may monitor you more closely for side effects if you take these or other medicines with Welireg. In some cases, they may lower your Welireg dose. Tell your health care provider right away if you notice any new or worsening side effects.
Hormonal birth control
Welireg can make hormonal birth control less effective. This may raise the risk of unintended pregnancy or breakthrough bleeding.
Examples of hormonal birth control include birth control pills, patches, vaginal rings, injections, or implants.
Warning: Because Welireg can harm a fetus, it is important to use effective birth control if you can get pregnant while taking Welireg. People who can become pregnant should use effective nonhormonal birth control (such as condoms, diaphragms, or copper IUDs) while taking Welireg and for one week after the last dose. Men with partners who can become pregnant should also use effective contraception during this time.
Talk with your health care provider about which birth control options may be right for you.
Other medicines that may not work as well with Welireg
Welireg can lower the levels of certain other medicines in the body, making them less effective. For some medicines, such as warfarin, even a small drop in levels can affect how well they work.
Your health care provider may avoid certain combinations, monitor you more closely, or adjust doses if needed.
Reducing Your Risk of Side Effects and Interactions
You can lower your risk of side effects and interactions by taking Welireg exactly as prescribed and keeping all recommended appointments for blood tests and oxygen monitoring.
The following steps may also help lower your risk:
- Take Welireg at the same time each day.
- Swallow the tablets whole. Do not crush, chew, or split them.
- Tell your health care provider and pharmacist about all medicines and supplements you use.
- Keep track of new or worsening symptoms and report them promptly.
Do not start, stop, or change medicines without talking to your health care provider first.
