Abemaciclib

Pronunciation: a-BEM-a-SYE-klib
Generic name: abemaciclib
Brand name: Verzenio
Dosage form: oral tablet
Drug class: CDK 4/6 inhibitors

Medically reviewed by Carmen Pope, BPharm. Last updated on Jan 19, 2025.

What is abemaciclib?

Abemaciclib is used to treat HR-positive and HER2-negative breast cancer in adults. It is a targeted treatment, not a chemotherapy drug (see Is Verzenio (abemaciclib) a chemo drug?). 

Abemaciclib (brand name Verzenio) first gained FDA approval on September 28, 2017. There is no generic Verzenio.

Uses and FDA approvals

Abemaciclib is a prescription medicine approved to treat various types of hormone receptor-positive (HR+), human epidermal growth factor receptor 2 negative (HER2–) breast cancer, such as:

• Early breast cancer that is HR+, HER2– node-positive and has a high risk of coming back in combination with endocrine therapy (tamoxifen or an aromatase inhibitor) 
• HR+, HER2– breast cancer that has worsened or spread (metastasized) in combination with an aromatase inhibitor (such as anastrozole, exemestane, or letrozole) as the first endocrine-based therapy
• HR+, HER2– breast cancer that has worsened or metastasized, and progressed despite endocrine therapy in combination with Fulvestrant.

Clinical trials have also reported abemaciclib is effective when used alone to treat HR+, HER2– breast cancer that has worsened, metastasized, or progressed despite endocrine treatment and chemotherapy.

Abemaciclib side effects

Most common side effects

Common side effects that patients may experience while taking abemaciclib are:

Digestive system effects

• Nausea and vomiting
• Abdominal pain
• Decreased appetite

Blood-related side effects

• Anemia (low red blood cell count)
• Leukopenia (low white blood cell count)
• Thrombocytopenia (low platelet count)

Other frequent side effects

• Increased risk of infections
• Fatigue and tiredness
• Headaches
• Alopecia (hair thinning or hair loss).

Important note for male patients

Male patients should be aware that clinical trials have shown that abemaciclib may affect their fertility and their ability to father a child. If you have concerns about fertility, talk to your healthcare provider before starting treatment.

Related/similar drugs

Serious side effects and warnings

Abemaciclib may cause the following serious side effects:

Diarrhea

Diarrhea is common with abemaciclib and may sometimes be severe. It may cause dehydration or increase your risk of an infection. Diarrhea is more likely to happen in the first month of taking abemaciclib. Tell your healthcare provider as soon as possible if you have any loose stools and start taking an antidiarrheal medicine (such as loperamide). Drink fluids to prevent dehydration.

Low white blood cell counts (neutropenia)

Low white blood cell counts may cause serious infections that can lead to death. Your healthcare provider should check your white blood cell counts before and during treatment with abemaciclib. Tell your healthcare provider right away if you have signs and symptoms of low white blood cell counts or develop symptoms of an infection.

Lung problems

Abemaciclib may cause severe or life-threatening inflammation of the lungs that could be fatal. Tell your healthcare provider right away if you have any new or worsening lung symptoms, including:

• trouble breathing or shortness of breath
• cough with or without mucus
• chest pain.

Liver problems

Abemaciclib can cause serious liver problems. Tell your healthcare provider right away if you have any of the following signs and symptoms of liver problems:

• feeling very tired
• pain on the upper right side of your stomach area (abdomen)
• loss of appetite
• bleeding or bruising more easily than normal.

Your healthcare provider will do blood tests to monitor your liver for elevations in liver enzymes during treatment with abemaciclib, such as alkaline phosphatase or alanine aminotransferase (ALT).

Blood clots in your veins, or the arteries of your lungs

Abemaciclib may cause serious blood clots that may be fatal. Tell your healthcare provider right away if you get any of the following signs and symptoms of a blood clot:

• pain or swelling in your arms or legs
• shortness of breath
• chest pain
• tachycardia (a fast heartbeat).

Allergic reactions

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

These are not all the possible side effects of abemaciclib. For more information, ask your healthcare provider or pharmacist. Call your healthcare provider for medical advice about side effects. You may report side effects to the FDA at 1-800-FDA-1088.

How does abemaciclib work?

Abemaciclib's mechanism of action involves blocking proteins involved in cell division called cyclin-dependent kinases (CDK), specifically CDK 4 and 6. Blocking these prevents cancer cells from dividing and multiplying uncontrollably because HR+ breast cancer cells rely heavily on CDK 4/6 for growth.

Abemaciclib belongs to the drug class called CDK 4/6 inhibitors.

How much does abemaciclib cost?

The cost of abemaciclib depends on your insurance plan and if you are eligible for the Verzenio (abemaciclib) savings card. Some people with commercial insurance who meet other criteria pay as little as $0 a month. Abemaciclib is only available through a specialty pharmacy that can help you work out if you are eligible for the savings card. For more information, call 1-844-ABEMACICLIB (1-844-837-9364).

If you do not have insurance or your insurance does not cover abemaciclib, you may pay close to the list price for it. See Verzenio (abemaciclib) Prices, Coupons, Copay Cards & Patient Assistance for more information.

Before taking this medicine

Do not take abemaciclib if you are allergic to abemaciclib, Verzenio, or any of the inactive ingredients in the Verzenio tablets.

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

• have a fever, chills, or other signs of infection
• have lung or breathing problems
• have a history of blood clots in your veins
• have liver or kidney problems
• take any medications, such as ketoconazole, clarithromycin, itraconazole, lopinavir/ritonavir, posaconazole, and voriconazole because these may affect abemaciclib concentrations
• are pregnant or intending to become pregnant
• are breastfeeding or intend to breastfeed.

Pregnancy

Abemaciclib may harm an unborn baby. For females who can become pregnant, your healthcare provider will do a pregnancy test before you start treatment with abemaciclib. You should use effective birth control (contraception) during treatment with abemaciclib and for 3 weeks after the last dose of abemaciclib. Tell your healthcare provider right away if you become pregnant or think you are pregnant during treatment with abemaciclib.

Breastfeeding

You should not breastfeed while using this medicine and for at least 3 weeks after your last dose.

Male fertility

It may be harder for males to get a woman pregnant if they are taking abemaciclib.

How should I take abemaciclib?

Take abemaciclib exactly as prescribed by your doctor. Follow all directions on your Verzenio (abemaciclib) Package Insert and read all medication guides or instruction sheets. Your doctor may occasionally change your dose.

• Abemaciclib is usually taken 2 times a day.
• Take with or without food, at the same time each day.
• Swallow whole and do not crush, chew, or break it. Do not take a cracked, broken, or damaged tablet.
• If you vomit shortly after taking abemaciclib, do not take another dose. Take your next dose as scheduled.

Call your doctor if you get loose stools (diarrhea) while taking abemaciclib and start taking anti-diarrhea medicine such as loperamide (Imodium A-D). Drink extra fluids to prevent dehydration.

Your blood will need to be tested often and your cancer treatments may be delayed based on the results.

Abemaciclib is taken until your breast cancer gets worse despite treatment or side effects become intolerable (see How long do you take Verzenio (abemaciclib) for?).

Abemaciclib dosing information

Usual Adult Dose of Abemaciclib for Breast Cancer:

• Abemaciclib 150 mg 2 times a day when used with fulvestrant, tamoxifen, or an aromatase inhibitor.
• Abemaciclib 200 mg 2 times a day when used alone.

What happens if I miss a dose?

Take abemaciclib as soon as you can, but skip the missed dose if it is almost time for your next dose. Do not take two doses at one time.

If you vomit shortly after taking abemaciclib, do not take another dose. Take your next dose as scheduled.

What happens if I overdose?

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

What should I avoid while taking abemaciclib?

Avoid taking ketoconazole during treatment with abemaciclib. Tell your healthcare provider if you take a medicine that contains ketoconazole.

Avoid grapefruit and products that contain grapefruit during treatment with abemaciclib. Grapefruit may increase levels of this medicine in your blood.

What other drugs will affect abemaciclib?

Sometimes it is not safe to use certain medicines at the same time. Some drugs can affect your blood levels of other drugs you use, which may increase side effects or make the medicines less effective.

Tell your doctor about all your other medicines, especially ketoconazole. You should not take ketoconazole while you are being treated with abemaciclib.

• Ketoconazole is a strong CYP3A4 inhibitor and coadministration of abemaciclib with strong CYP3A4 inhibitors should be avoided because they can increase abemaciclib concentrations.
• Other medications that are strong CYP3A4 inhibitors include clarithromycin, itraconazole, lopinavir/ritonavir, posaconazole, and voriconazole. Grapefruit or grapefruit juice should also be avoided.

The dose of abemaciclib should be reduced if co-administered with moderate CYP3A4 inhibitors, such as
verapamil or diltiazem.

This list is not complete, see the Verzenio (abemaciclib) Prescribing Information for a full list. Other drugs may affect abemaciclib, including prescription and over-the-counter medicines, vitamins, and herbal products. Not all possible drug interactions are listed here.

Ingredients

Abemaciclib is only available under the brand name Verzenio. There is no abemaciclib generic.

Active ingredient: abemaciclib

Inactive ingredients: microcrystalline cellulose 102, microcrystalline cellulose 101, lactose monohydrate, croscarmellose sodium, sodium stearyl fumarate, and silicon dioxide.

Color mixture ingredients: polyvinyl alcohol, titanium dioxide, polyethylene glycol, talc, iron oxide yellow, iron oxide red.

Abemaciclib is available as 50 mg, 100 mg, 150 mg, and 200 mg tablets.

Abemaciclib storage

Store abemaciclib at room temperature between 68°F to 77°F (20°C to 25°C).

Keep out of the reach of children.

Who makes abemaciclib?

Abemaciclib is manufactured by Eli Lilly and Company (commonly known as Lilly), headquartered in Indianapolis, Indiana. Besides abemaciclib, Lilly produces several other notable medications including:

• Cymbalta (duloxetine) for depression and anxiety
• Humalog and Lyumjev for diabetes
• Taltz for psoriasis and psoriatic arthritis
• Olumiant for rheumatoid arthritis
• Jardiance (in partnership with Boehringer Ingelheim) for diabetes
• Mounjaro (tirzepatide) for type 2 diabetes and weight management
• Zepbound (tirzepatide) for weight management.

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