Pronunciation: Well-ih-reg
Generic name: belzutifan
Dosage form: tablet (40mg)
Drug class: Miscellaneous antineoplastics

Medically reviewed by Melisa Puckey, BPharm. Last updated on Jan 5, 2024.

What is Welireg?

Welireg (belzutifan) is used in the treatment of von Hippel-Lindau (VHL) disease to help reduce the size of tumors, including tumors in the brain and spinal cord called central nervous system hemangioblastomas, pancreatic neuroendocrine tumors, and renal cell carcinomas. Welireg is also used to treat advanced renal cell carcinoma (RCC) in certain adults.

Von Hippel-Lindau (VHL) disease is a rare genetic disorder that causes cysts, benign tumors, and malignant tumors to grow in the body due to a mutation in the Von Hippel–Lindau tumor suppressor gene. This change in the gene causes an accumulation in the protein HIF-2a, which is associated with tumor growth.

Welireg is a hypoxia-inducible factor (HIF) inhibitor that works by blocking HIF-2a, to help reduce tumor growth.

Welireg is manufactured for Merck Sharp & Dohme Corp.

What is Welireg used for?

Welireg received FDA approval on August 13, 2021, to treat adult patients with von Hippel-Lindau (VHL) disease who do not require immediate surgery but require therapy for central nervous system (CNS) hemangioblastomas, pancreatic neuroendocrine tumors (pNET), or renal cell carcinoma (RCC). Welireg is manufactured for Merck Sharp & Dohme Corp.

On December 14,2023, Welireg received FDA approval for the treatment of adult patients with advanced renal cell carcinoma (RCC) following a programmed death receptor-1 (PD-1) or programmed death-ligand 1 (PD-L1) inhibitor and a vascular endothelial growth factor tyrosine kinase inhibitor (VEGF-TKI). 

Welireg side effects

Common Welireg side effects when taken for VHL disease may include lower hemoglobin, headache, dizziness, tiredness, nausea, increased blood sugar (increased thirst or urination, dry mouth, fruity breath), or abnormal kidney function tests.

Common Welireg side effects when taken for advanced RCC may include decreased hemoglobin, tiredness, muscle, and joint pain, changes in laboratory readings, increased creatinine, decreased lymphocytes, increased alanine aminotransferase, decreased sodium, increased potassium, and increased aspartate aminotransferase. 

Serious Welireg side effects 

Get emergency medical help if you have signs of an allergic reaction: hives, difficulty breathing, swelling of your face, lips, tongue, or throat.

Call your doctor right away if you have:

• low red blood cells (anemia) - pale skin, tiredness, feeling light-headed or short of breath, cold hands and feet; or
• low oxygen levels - shortness of breath, chest pain, fast heartbeats; or
• vision problems

Welireg may also cause the serious side effects of pneumonia, hemorrhage, and pleural effusion, sepsis and hemorrhage. 

Your cancer treatments may be delayed or permanently discontinued if you have certain side effects.

Welireg may cause other serious side effects included in the Warnings section.

This is not a complete list of side effects, and others may occur. Call your doctor for medical advice about side effects. You may report side effects to the FDA at 1-800-FDA-1088.

Warnings

Welireg can cause anemia (low red blood cells) or low oxygen levels. These conditions may need to be treated with blood transfusions, oxygen therapy, or hospitalization. You will have blood tests to check your red blood cell counts before you start and during treatment. Tell your healthcare provider if you get any symptoms of low red blood cell counts, including tiredness, feeling cold, shortness of breath, chest pain, or fast heartbeat.

Welireg may harm an unborn baby. Both men and women should use effective non-hormonal birth control to prevent pregnancy while using Welireg and for at least 1 week after the last dose. See ‘Before taking this medication’ section for more information on pregnancy and breastfeeding.

Before taking this medicine

Before taking Welireg, tell your healthcare provider about all of your medical conditions, including if you:

• have low red blood cell counts (anemia).

Pregnancy

Tell your healthcare provider if you are pregnant or plan to become pregnant, as Welireg may harm an unborn baby if the mother or father is using this medicine. Both men and women should use effective non-hormonal birth control to prevent pregnancy while using Welireg and for at least 1 week after the last dose.

Females who are able to become pregnant 

• You should do a pregnancy test before you start treatment with Welireg to exclude pregnancy.
• Birth control methods that contain hormones (such as birth control pills, injections, or transdermal system patches) may not work as well during treatment with Welireg.
• Talk to your healthcare provider about birth control methods that may be right for you during treatment with Welireg.
• Tell your healthcare provider right away if you become pregnant or think you may be pregnant during treatment.

Males with female partners who are able to become pregnant:

• You should use effective birth control (contraception) during treatment with Welireg and for 1 week after your last dose.
• Tell your healthcare provider right away if your partner becomes pregnant or thinks she is pregnant while you are taking Welireg.

Fertility

Welireg may cause fertility problems in males and females, which may affect your ability to have children. The reversibility of the effect on fertility is unknown. Talk to your healthcare provider if this is a concern for you. 

Using Welireg with hormonal contraceptives may stop the hormonal contraceptive from working (contraceptive failure).

Breastfeeding 

Do not breastfeed while using this medicine, and for at least 1 week after your last dose.

How should I take Welireg?

Follow all directions on your prescription label and read all medication guides or instruction sheets. Your doctor may occasionally change your dose. Use the medicine exactly as directed.

Welireg directions

• Take Welireg tablets once daily at the same time each day, with or without food.
• Swallow the tablet whole, and do not crush, chew, or break it.
• If you vomit shortly after taking tablets, do not take another dose. Take your next dose as scheduled.

Welireg can cause anemia (low red blood cells) or low oxygen levels. These conditions may need to be treated with blood transfusions, oxygen therapy, or hospitalization.

You will need frequent medical tests, even if you have no symptoms.

Do not change your dose or stop using a medicine without your doctor's advice.

Dosing information

Usual Adult Welireg Dose: 120 mg orally once daily until disease progression or unacceptable toxicity.  The dose may be changed due to side effects.

Welireg is available as 40mg tablets.

What happens if I miss a dose?

If you miss a dose, take it as soon as possible on the same day. Then take your next dose at your regular time the next day. Do not take extra tablets to make up for the missed dose.

What happens if I overdose?

Seek emergency medical attention or call the Poison Help line at 1-800-222-1222.

What other drugs will affect Welireg?

Many drugs can interact with Welireg, and some drugs should not be used at the same time. Tell your doctor about all other medicines you use. This includes prescription and over-the-counter medicines, vitamins, and herbal products.

Using Welireg with hormonal contraceptives may stop the hormonal contraceptive from working or there may be an increase in breakthrough bleeding.

Not all possible interactions are listed here, click the link below to check for drug interactions.

Storage

• Store at room temperature between 68°F to 77°F (20°C to 25°C).
• The bottle contains 2 desiccant canisters that help keep your medicine dry. Do not eat the desiccant canisters.

Ingredients

Active ingredient: belzutifan
Inactive ingredients: croscarmellose sodium, hypromellose acetate succinate, magnesium stearate, mannitol, microcrystalline cellulose, and silicon dioxide. 

The film-coating contains FD&C Blue #2 aluminum lake, polyethylene glycol, polyvinyl alcohol, talc, and titanium dioxide.

Company

Manufactured for Merck Sharp & Dohme.

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Medical Disclaimer