Abemaciclib
CDK4/6 inhibitors
CDK4/6 inhibitorsHigh alert
An error with this medicine can cause serious harm: double checks and protocols are used.Pregnancy: avoid
Avoid in pregnancy. Can harm the fetus: a pregnancy test is done before starting, effective contraception is used during treatment and for a time afterwards (by women and by men…
A CDK4/6 inhibitor for HR-positive, HER2-negative breast cancer, with hormone therapy or alone. Its hallmark is diarrhoea, often early.
Quick facts
- Group
- CDK4/6 inhibitors
- Target
- Cyclin-dependent kinases 4 and 6 (CDK4/6)
- Used for
- HR-positive · Advanced or metastatic HR-positive
- Key effects
- Diarrhoea · Neutropenia · Nausea
- Monitor
- Complete blood count · Liver tests
- ATC
- L01EF03
No doses: the clinician sets them by the current guideline.
Mechanism of action
The figure shows abemaciclib in the ATP pocket of human CDK6.
Abemaciclib inhibits CDK4 and CDK6, keeps Rb active and stops hormone receptor-positive breast cancer cells in G1. It is the only member of the class that is also used on its own after endocrine therapy and chemotherapy.
- Inhibits CDK4 and CDK6
- Rb stays active: G1 arrest of HR-positive cells
- With endocrine therapy, or alone after chemotherapy
Indications
- HR-positive, HER2-negative, node-positive early breast cancer at high risk of recurrence, with tamoxifen or an aromatase inhibitor. Breast cancer →
- Advanced or metastatic HR-positive, HER2-negative breast cancer: with an aromatase inhibitor first line, with fulvestrant after endocrine therapy, or alone after endocrine therapy and chemotherapy. Breast cancer →
Adverse effects
Common
- Diarrhoea, very common and sometimes severe
- Neutropenia, anaemia and thrombocytopenia
- Nausea, vomiting, abdominal pain, decreased appetite
- Fatigue and infections
- Hair loss and headache
Contraindications
- No absolute contraindications in the label apart from hypersensitivity; see the warnings
Key interactions
- Strong CYP3A4 inhibitors (clarithromycin, itraconazole, ketoconazole, ritonavir) and grapefruit
- Raise abemaciclib levels; strong inhibitors are avoided.
- Strong CYP3A4 inducers (rifampicin, carbamazepine, phenytoin, St John's wort)
- Lower its levels and can make it fail.
What is monitored
- Complete blood count
- Liver tests
- Stool frequency and hydration
- Signs of venous thrombosis (leg swelling, chest pain, breathlessness)
Administration and safety
- Oral; swallowed whole, never split, crushed, chewed or opened.
- Grapefruit, its juice and St John's wort are avoided because they change its levels.
- An antidiarrhoeal plan is given at the start: fluids and antidiarrhoeal medicine at the first loose stool, as the doctor directs.
Pregnancy and breastfeeding
Avoid in pregnancy. Can harm the fetus: a pregnancy test is done before starting, effective contraception is used during treatment and for a time afterwards (by women and by men with partners who could conceive), and breastfeeding is avoided.
Nursing care
- Teach the diarrhoea plan before the first dose and how to recognise dehydration (thirst, dry mouth, little urine, fast pulse).
- Review blood counts and liver tests as ordered.
- Ask about history of blood clots; teach signs of thrombosis.
- Confirm a negative pregnancy test before the first dose and teach contraception during treatment and afterwards.
Pharmacokinetics
- Absorption
- Oral tablets, with or without food.
- Metabolism
- Liver, CYP3A.
- Half-life
- About 18 hours.
Test yourself
Think of the answer, then tap the question to see it.
Which adverse effect is most characteristic of abemaciclib?
Diarrhoea, often early and sometimes severe.
Which CDK4/6 inhibitor can be given without endocrine therapy?
Abemaciclib, alone after endocrine therapy and chemotherapy for metastatic disease.
What should the patient have at home when starting abemaciclib?
An antidiarrhoeal medicine and a plan to start it, with fluids, at the first loose stool.
Connections
← Back to the class: CDK4/6 inhibitors
Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.
Sources: Abemaciclib: MedlinePlus Drug Information (MedlinePlus (U.S. National Library of Medicine), 2023); Abemaciclib - NCI (National Cancer Institute, 2024); ATCDDD - ATC/DDD Index (WHO Collaborating Centre for Drug Statistics Methodology, 2026).
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Representative model, for educational purposes only.