Palbociclib (Ibrance), ribociclib (Kisqali) and abemaciclib (Verzenio) belong to the same family of breast cancer tablets, called CDK4/6 inhibitors. They are used together with hormone therapy for hormone receptor-positive (HR-positive), HER2-negative breast cancer. They work in the same basic way, but the schedules, side effects and checks are different. This guide sets out what you can expect from each.
What CDK4/6 inhibitors do
CDK4 and CDK6 are proteins that push cancer cells to grow and divide. These medicines block those proteins, which aims to slow or stop the growth of the cancer5. In lab studies, palbociclib stopped breast cancer cells moving on to the stage where they copy themselves1. They are a type of targeted cancer drug, not chemotherapy5.
Why they are taken with hormone therapy
HR-positive breast cancer uses the hormone oestrogen to grow. CDK4/6 inhibitors are licensed together with hormone therapy, usually an aromatase inhibitor (such as letrozole or anastrozole) or fulvestrant134. Abemaciclib can also be used with tamoxifen after surgery for early breast cancer4. Women who have not been through the menopause, and men, also need a medicine that switches off hormone production from the ovaries or testicles (an LHRH or GnRH agonist)34.
For more on the hormone tablets themselves, see our guide to letrozole, anastrozole or tamoxifen.
The three medicines at a glance
| Palbociclib (Ibrance) | Ribociclib (Kisqali) | Abemaciclib (Verzenio) | |
|---|---|---|---|
| Usual dose | 125 mg once a day1 | 600 mg once a day (advanced); 400 mg once a day (early)3 | 150 mg twice a day4 |
| Schedule | 21 days on, 7 days off1 | 21 days on, 7 days off3 | Every day, no break4 |
| Food | Tablets: with or without food. Capsules: with food12 | With or without food3 | With or without food4 |
| Licensed in the US for | Advanced or spread (metastatic) breast cancer1 | Advanced breast cancer, and high-risk early breast cancer after surgery3 | Advanced breast cancer, and high-risk early breast cancer after surgery4 |
| Main side effect to watch | Low white blood cells1 | Heart rhythm, liver and low white blood cells3 | Diarrhoea4 |
One practical point for palbociclib: check which form you have. Capsules should be taken with food, while Ibrance tablets can be taken with or without food12. Take your dose at about the same time each day, and swallow the tablets whole1.
Side effects compared
Palbociclib (Ibrance)
The most common side effects are low blood counts (especially white blood cells, which fight infection), infections, tiredness, nausea, mouth sores, diarrhoea and hair thinning or hair loss1. Low white cells are the main reason for blood tests and dose changes1.
Ribociclib (Kisqali)
Ribociclib also lowers white cells, and it has some extra risks3:
- Heart rhythm. It can change the heart’s electrical rhythm (QT prolongation), so you need a heart tracing (ECG) before you start and again around day 14. It is not used with tamoxifen, and other medicines that affect heart rhythm should be avoided.
- Liver. Liver blood tests can rise, and liver injury has been reported.
- Skin. Rare but serious skin reactions can happen; stop and get help for a widespread rash with blisters or peeling.
Other common side effects include infections, nausea, tiredness, diarrhoea, headache, hair loss, cough and rash3.
Abemaciclib (Verzenio)
Diarrhoea is the side effect most people notice. Most people who get it do so in the first month. The label advises starting an anti-diarrhoea medicine such as loperamide at the first loose stool, drinking more fluids, and telling your team4. Other common side effects are infections, low white cells, tiredness, stomach pain, nausea, anaemia and vomiting. Raised liver tests and blood clots in the veins can also happen: get help quickly for pain or swelling in an arm or leg, sudden breathlessness or chest pain4.
For all three
- Lung inflammation (pneumonitis) is rare but can be serious. Tell your team about a new or worse cough, breathlessness or chest pain134.
- Infection. Contact your cancer advice line straight away if your temperature is 37.5°C or above, or below 36°C5. Also report chills, dizziness, weakness, or bleeding or bruising easily1.
Blood tests and checks
- Palbociclib: a full blood count before you start, at the start of each cycle, and on day 15 of the first two cycles1.
- Ribociclib: blood counts and liver tests before you start, every two weeks for the first two cycles, then at the start of the next four cycles; plus ECGs3.
- Abemaciclib: blood counts and liver tests before you start, every two weeks for the first two months, then monthly for the next two months4.
If side effects are hard to manage, the usual answer is a pause and a lower dose rather than stopping altogether. All three labels set out dose reductions for this134. Do not change the dose yourself.
Missed or vomited doses
With palbociclib and ribociclib, if you miss a dose or are sick after taking it, do not take an extra dose. Take the next dose at the usual time13. Ask your pharmacist what to do for abemaciclib, which is taken twice a day.
Grapefruit and other medicines
All three are broken down by the same liver enzyme (CYP3A). Some antibiotics, antifungals and HIV medicines can raise their levels, and some epilepsy medicines, the antibiotic rifampicin and the herbal remedy St John’s wort can lower them134. The labels for palbociclib and abemaciclib say to avoid grapefruit and grapefruit juice14. Ribociclib also needs care with any medicine that can affect heart rhythm3. Give your team a full list of what you take, including over-the-counter and herbal products.
How long you take them
- Advanced breast cancer: you usually keep taking it for as long as it is working and the side effects are manageable54.
- Early breast cancer: ribociclib is taken for 3 years and abemaciclib for 2 years, unless the cancer comes back or side effects stop treatment first34.
If the cancer starts to grow, your team will look at the next options. Tests on the cancer’s genes, such as for PIK3CA or ESR1 changes, can open up other treatments14. Our guide to when a cancer medicine stops working explains how these decisions are made.
Pregnancy and contraception
All three can harm an unborn baby. Women who could become pregnant should use effective contraception during treatment and for at least 3 weeks after the last dose134. Men taking palbociclib with a partner who could become pregnant should use contraception for 3 months after the last dose1.
Generic versions and cost
Generic palbociclib contains the same active ingredient as Ibrance. If you switch, check whether you have tablets or capsules, as the food rule differs. Our generic Ibrance and generic Verzenio pages explain the options.
We stock palbociclib, including Palnat 125 mg capsules, Palboxen 125 mg capsules and Ibrance 125 mg tablets. See all options on our palbociclib and abemaciclib pages, or browse our breast cancer medicines. All need a prescription. We do not currently supply ribociclib.
Frequently asked questions
How long can you take palbociclib?
For advanced breast cancer, usually for as long as it keeps the cancer under control and the side effects are manageable. There is no fixed end date, and your team reviews it with scans and blood tests.
Does Ibrance cause hair loss?
Hair thinning or hair loss is one of the more common side effects of palbociclib. Hair usually grows back once treatment finishes.
Is palbociclib chemotherapy?
No. Palbociclib is a targeted cancer drug that blocks the CDK4 and CDK6 proteins. It is taken with hormone therapy. See our guide is it chemotherapy?
Is Ibrance or Kisqali better?
Neither is simply better. They are licensed for slightly different situations and have different side effects and checks. For example, ribociclib needs heart tracings and is not used with tamoxifen. Your cancer team will match the choice to your stage and your health.
What happens when Ibrance stops working?
Your team will review your scans and may test the cancer’s genes. Depending on the results, they may suggest a different hormone therapy, a different targeted medicine or chemotherapy.
Sources & references
- US National Library of Medicine, DailyMed. Ibrance (palbociclib) tablets prescribing information.
- US National Library of Medicine, DailyMed. Ibrance (palbociclib) capsules prescribing information.
- US National Library of Medicine, DailyMed. Kisqali (ribociclib) prescribing information.
- US National Library of Medicine, DailyMed. Verzenio (abemaciclib) prescribing information.
- Cancer Research UK. Palbociclib (Ibrance). Last reviewed 21 February 2024.
Related reading
- Biosimilars vs generics in cancer care
- Letrozole, anastrozole or tamoxifen?
- Is it chemotherapy?
- When a cancer medicine stops working
This content is for informational purposes only and is not medical advice. Cancer treatment decisions should be made with your oncologist, and you should not change or stop any medicine without talking to them. Used as prescribed by a licensed medical professional.
Nancy Kapadia is a licensed clinical pharmacist with 10 years of experience. She holds a B.Pharm from Baba Farid University. At OnlineMeds, she reviews medicine and health content to help ensure it is accurate, evidence-based, and easy to understand.