Abemaciclib

Abemaciclib is used to treat hormone receptor (HR)-positive, human epidermal growth factor receptor 2 (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. Its use in combination with imlunestrant was approved on September 18, 2026. There is no generic Verzenio.

Abemaciclib is a prescription medicine approved to treat adults with the following types of breast cancer:

• HR-positive, HER2-negative, node-positive early breast cancer that has a high risk of coming back, in combination with endocrine therapy (tamoxifen or an aromatase inhibitor)
• HR-positive, HER2-negative advanced or metastatic breast cancer, in combination with an aromatase inhibitor (such as anastrozole or letrozole) as the first endocrine-based therapy
• HR-positive, HER2-negative advanced or metastatic breast cancer that has progressed after endocrine therapy, in combination with fulvestrant
• Estrogen receptor (ER)-positive, HER2-negative, estrogen receptor-1 (ESR1)-mutated advanced or metastatic breast cancer that has progressed after at least 1 line of endocrine therapy, in combination with imlunestrant. Your healthcare provider will use an FDA-authorized blood test to check for an ESR1 mutation before you start this combination.
• HR-positive, HER2-negative advanced or metastatic breast cancer that has progressed after endocrine therapy and prior chemotherapy for metastatic disease, when used alone (monotherapy).

Take abemaciclib exactly as prescribed by your doctor. Follow all directions on your Verzenio (abemaciclib) Patient Information and read all medication guides or instruction sheets. Your doctor may change your dose if needed. Do not stop taking abemaciclib or change the dose without talking to your doctor.

• Abemaciclib is usually taken 2 times a day, at about the same times every day.
• Take with or without food.
• Swallow whole. Do not chew, crush, or split the tablet. Do not take a tablet that is broken, cracked, or damaged.
• If you vomit after taking abemaciclib, do not take another dose. Take your next dose at your regular time.

When abemaciclib is used with fulvestrant, tamoxifen, imlunestrant, or an aromatase inhibitor, also read the Patient Information or Medication Guide for that medicine.

Call your doctor if you get loose stools (diarrhea) while taking abemaciclib and start taking an 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 treatment may be paused, delayed, or your dose lowered based on the results. Blood counts and liver tests are checked before you start, every 2 weeks for the first 2 months, monthly for the next 2 months, and then as needed.

For early breast cancer, abemaciclib is taken for 2 years, unless the cancer comes back or side effects become intolerable. For advanced or metastatic breast cancer, it is taken until the cancer gets worse or side effects become intolerable (see How long do you take Verzenio (abemaciclib) for?).

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
• are pregnant or plan to become pregnant
• are breastfeeding or plan to breastfeed

Tell your healthcare provider about all the medicines you take, including prescription and over-the-counter medicines, vitamins, and herbal supplements. Especially tell your healthcare provider if you take a medicine that contains ketoconazole.

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. If you are taking abemaciclib in combination with another medicine, your healthcare provider will tell you how long you should use birth control. Tell your healthcare provider right away if you become pregnant or think you are pregnant during treatment with abemaciclib.

Breastfeeding

It is not known if abemaciclib passes into breast milk. Do not breastfeed while taking abemaciclib and for at least 3 weeks after your last dose. If you are taking abemaciclib in combination with another medicine, your healthcare provider will tell you how long you should not breastfeed.

Male fertility

Abemaciclib may affect a man's ability to father a child.

Most common side effects

The most common side effects of abemaciclib are:

• Digestive system effects diarrhea nausea and vomiting stomach area (abdominal) pain
• Blood-related side effects low white blood cell counts (neutropenia and leukopenia) low red blood cell counts (anemia)
• Other frequent side effectsinfectionstiredness (fatigue)decreased appetiteheadachehair thinning or hair loss (alopecia)low platelet count (thrombocytopenia).

Abemaciclib can also raise a blood test called serum creatinine, usually within the first month of treatment. This does not mean your kidneys are damaged. It happens because abemaciclib blocks the way the kidneys release creatinine into the urine, and levels return to normal after treatment stops. Your healthcare provider may use other tests, such as cystatin C or BUN, to check your kidney function.

Important note for male patients

Based on animal studies, abemaciclib may affect fertility in males and their ability to father a child. If you have concerns about fertility, talk to your healthcare provider before starting treatment.

Serious side effects and warnings

Abemaciclib may cause the following serious side effects:

Diarrhea

Diarrhea is common with abemaciclib and may sometimes be severe. Diarrhea may lead to loss of large amounts of fluid and salt, causing dehydration. Diarrhea is most likely to happen in the first month of taking abemaciclib. If you have any loose stools, start taking an antidiarrheal medicine (such as loperamide), drink more fluids, and tell your healthcare provider right away.

Low white blood cell counts (neutropenia)

Low white blood cell counts are common during treatment with abemaciclib and 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 develop signs or symptoms of an infection, such as fever and chills.

Lung problems

Abemaciclib may cause severe or life-threatening inflammation of the lungs that can lead to death. Tell your healthcare provider right away if you have any new or worsening signs or symptoms, including:

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

Liver problems

Abemaciclib can cause serious liver problems. Your healthcare provider should do blood tests to check your liver (ALT, AST, and bilirubin) before and during treatment with abemaciclib. Tell your healthcare provider right away if you have signs and symptoms of liver problems, such as:

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

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

Abemaciclib may cause serious blood clots that have led to death. Tell your healthcare provider right away if you develop signs or symptoms of a blood clot, such as:

• pain or swelling in your arms or legs
• shortness of breath
• chest pain
• rapid breathing
• rapid heart rate

If you develop serious side effects during treatment with abemaciclib, your healthcare provider may reduce your dose, temporarily stop, or completely stop treatment.

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.

Abemaciclib works by blocking two enzymes involved in cell division called cyclin-dependent kinases 4 and 6 (CDK4 and CDK6). In estrogen receptor-positive breast cancer cells, these enzymes help switch on a protein called retinoblastoma protein (Rb), which allows cells to move through the cell cycle and divide. By blocking CDK4 and CDK6, abemaciclib stops cancer cells from moving from the growth phase (G1) into the phase where they copy their DNA (S phase), causing the cells to stop dividing or die.

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

The cost of abemaciclib depends on your insurance plan and whether 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. People with government insurance, such as Medicare, Medicaid, VA, or TRICARE, are not eligible. Abemaciclib is dispensed by a specialty pharmacy, which can help you work out if you are eligible for the savings card. For more information, call Lilly Support Services at 1-800-LillyRx (1-800-545-5979).

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.

Usual Adult Dose of Abemaciclib for Breast Cancer:

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

Premenopausal and perimenopausal women and men who take abemaciclib with an aromatase inhibitor, imlunestrant, or fulvestrant should also receive a gonadotropin-releasing hormone (GnRH) agonist.

If side effects occur, the dose may be lowered in 50 mg steps. Abemaciclib is stopped if a dose of 50 mg 2 times a day cannot be tolerated. People with severe liver impairment (Child-Pugh C) take abemaciclib once a day instead of twice a day.

Skip the missed dose and take your next dose at your regular time. Do not take two doses at one time.

If you vomit after taking abemaciclib, do not take another dose. Take your next dose at your regular time.

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

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 the amount of abemaciclib in your blood.

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.

Abemaciclib is broken down mainly by the liver enzyme CYP3A4. Tell your doctor about all your other medicines, especially ketoconazole.

• Ketoconazole is a strong CYP3A inhibitor that is predicted to increase abemaciclib levels by up to 16-fold. You should not take ketoconazole while you are being treated with abemaciclib.
• Other strong CYP3A inhibitors, such as clarithromycin, also increase abemaciclib levels. Your abemaciclib dose will be reduced if you need to take one of these medicines.
• Moderate CYP3A inhibitors, such as verapamil and diltiazem, may also increase abemaciclib levels. Your healthcare provider will monitor you for side effects and may lower your abemaciclib dose if needed.
• Strong or moderate CYP3A inducers, such as rifampin, efavirenz, bosentan, and modafinil, lower abemaciclib levels and may make it work less well. These should be avoided.
• Grapefruit or grapefruit juice should also be avoided.

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

Store abemaciclib at room temperature between 68°F and 77°F (20°C and 25°C). Short periods between 59°F and 86°F (15°C and 30°C) are allowed.

Keep out of the reach of children.

Abemaciclib is made by Eli Lilly and Company (commonly known as Lilly), headquartered in Indianapolis, Indiana, and marketed in the US by Lilly USA, LLC.

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, and iron oxide red.

Abemaciclib is available as 50 mg, 100 mg, 150 mg, and 200 mg tablets, supplied in blister packs of 14 tablets (a 7-day supply).