Belzutifan (Welireg)
Belzutifan is a type of targeted cancer drug. You pronounce it as bell-zoo-tee-fan. It is also known as Welireg.
It is a treatment for people with certain 
caused by a rare inherited condition called .
People with VHL may have belzutifan if they can’t have, or don’t want surgery to remove:
- a type of cancerous kidney tumour called a renal cell carcinoma (kidney cancer)
- a non cancerous (benign) brain tumour called a haemangioblastoma
- a tumour in the cells that control how the pancreas works - called pancreatic neuroendocrine tumours or pancreatic NETs
How does belzutifan work?
Belzutifan is a type of targeted cancer drug. It is called a selective hypoxia-inducible factor 2 alpha (HIF-2 alpha) inhibitor.
VHL leads to an increase in the amount of HIF-2 alpha in the body. This causes changes in tumour cells that make them grow. Belzutifan blocks HIF-2 alpha and helps control the growth of the tumour cells.
How do you take belzutifan?
You take belzutifan as a tablet. You swallow it whole with a glass of water. You can take it with or without food.
You should take the right dose, not more or less.
Talk to your healthcare team before you stop taking a cancer drug, or if you miss a dose.
How often do you take belzutifan?
You usually take belzutifan once a day.
You take it for as long as it is working and the side effects aren’t too bad.
Tests
You have blood tests before and during your treatment. They check your levels of blood cells and other substances in the blood. They also check how well your liver and kidneys are working.
Before treatment starts you may have a blood test to check for viruses such as hepatitis B, hepatitis C, and . This is called a viral screen.
It’s important for your doctor to know if you have had any of these viruses. This is because this treatment can weaken your and can cause the virus to become active again (reactivation).
Your nurse checks the amount of oxygen in your blood before and during treatment. This is because belzutifan can affect your oxygen levels. They do this with a clip that they put on your finger.
If you are able to get pregnant, you are normally asked to have a pregnancy test.
What are the side effects of belzutifan?
Side effects can vary from person to person. They also depend on what other treatment you are having.
When to contact your team
Your doctor, nurse, or pharmacist will go through the possible side effects. They will monitor you closely during treatment and check how you are at your appointments. Contact your advice line as soon as possible if:
-
you have severe side effects
-
your side effects aren’t getting any better
-
your side effects are getting worse
Early treatment can help manage side effects better.
We haven't listed all the side effects here. Talk to your healthcare team if you have any new symptoms that you think might be a side effect of your treatment.
Remember it is very unlikely that you will have all of these side effects, but you might have some of them at the same time.
Common side effects
These side effects happen in more than 10 in 100 people (more than 10%). You might have one or more of them. They include:
Breathlessness and looking pale
You might be breathless and look pale due to a drop in red blood cells. This is called anaemia.
Difficulty breathing
You may have difficulty breathing.
Sometimes this can be caused by a low amount of oxygen in your blood (hypoxia). Your healthcare team will check your oxygen levels regularly.
Let your healthcare team know straight away if you are having difficulty breathing.
Tiredness and weakness (fatigue)
You might feel very tired and as though you lack energy.
Various things can help you to reduce tiredness and cope with it, for example exercise. Some research has shown that taking gentle exercise can give you more energy. It is important to balance exercise with resting.
Don’t drive or operate machinery if you feel very tired.
Feeling sick
Feeling or being sick is usually well controlled with anti sickness medicines. It might help to avoid fatty or fried foods, eat small meals and snacks and take regular sips of water. Relaxation techniques might also help.
It is important to take anti sickness medicines as prescribed even if you don’t feel sick. It is easier to prevent sickness rather than treat it once it has started.
Weight gain
You may gain weight while having this treatment. You may be able to control it with diet and exercise. Tell your healthcare team if you are finding it difficult to control your weight.
Possible rare and long term side effects
This is a new drug in cancer treatment. So there is limited information available at the moment about possible rare and longer term effects that it may cause. Tell your doctor if you notice anything that is not normal for you.
Coping with side effects
We have more information about side effects and tips on how to cope with them.
What else do you need to know?
Other medicines, food and drink
Cancer drugs can interact with medicines, herbal products, and some food and drinks. We are unable to list all the possible interactions that may happen. An example is grapefruit or grapefruit juice which can increase the side effects of certain drugs.
Tell your healthcare team about any medicines you are taking. This includes vitamins, herbal supplements and over the counter remedies. Also let them know about any other medical conditions or allergies you may have.
Loss of fertility
You may not be able to become pregnant or get someone pregnant after treatment with this drug. Talk to your doctor before starting treatment if you think you may want to have a baby in the future.
Men might be able to store sperm before starting treatment. And women might be able to store eggs or ovarian tissue. But these services are not available in every hospital, so you would need to ask your doctor about this.
Contraception and pregnancy
This treatment might harm a baby developing in the womb. It is important not to become pregnant or get someone pregnant while you're having treatment and for at least one week afterwards.
Belzutifan may stop hormone contraceptives working properly. This includes the contraceptive pill, injection or implant. Use a barrier method of contraception such as condoms during sex if you are using one of these.
If your partner is pregnant you should also use a barrier method of contraception during treatment and for one week after the last dose.
Talk to your doctor or nurse about effective contraception before starting treatment. Let them know straight away if you or your partner become pregnant while having treatment.
Breastfeeding
Don’t breastfeed during this treatment and for 1 week after your last dose, because the drug may come through into your breast milk.
Immunisations
Don’t have immunisations with live vaccines while you’re having treatment and for up to 12 months afterwards. The length of time depends on the treatment you are having.
Ask your doctor or pharmacist how long you should avoid live vaccinations.
In the UK, live vaccines include rubella, mumps, measles, BCG, and yellow fever.
You can usually have:
- other vaccines, but they might not give you as much protection as usual
- the flu vaccine (as an injection)
- the coronavirus (COVID-19) vaccine
Talk to your doctor or pharmacist about the best time to have a vaccine in relation to your cancer treatment.
Contact with others who have had immunisations
You can be in contact with other people who have had live vaccines as injections. If someone has had a live vaccine by mouth or nasal spray there may be a small risk the vaccine virus can be passed onto you if your is weakened.
Your healthcare team will let you know if you need to take any precautions if you are in close contact with someone who has had a live vaccine.
More information about this treatment
For further information about this treatment and possible side effects go to the electronic Medicines Compendium (eMC) website. You can find the patient information leaflet on this website.
You can report any side effect you have to the Medicines Health and Regulatory Authority (MHRA) as part of their Yellow Card Scheme.
