[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Pharmacology](https://durgical.com/en/pharmacology/) › [CDK4/6 inhibitors](https://durgical.com/en/pharmacology/classes/cdk4-6-inhibitors/) › Abemaciclib # Abemaciclib ## CDK4/6 inhibitors? CDK4/6 inhibitors ## High 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. Updated Nov 1, 2026 ## Quick facts **Group** [CDK4/6 inhibitors](https://durgical.com/en/pharmacology/classes/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. On this page - The basics Mechanism of action - Indications - Adverse effects - Pharmacokinetics - Memory aid - Clinical What the labels mean - Safety Contraindications - Key interactions - What is monitored - Administration and safety - Pregnancy and breastfeeding - Nursing care - Study Test yourself - Connections Connections ## Mechanism of action ✂**Cyclin-dependent kinases 4 and 6 (CDK4/6)**Abemaciclib ⓘ The figure shows abemaciclib in the ATP pocket of human CDK6. **Target in 3D:** Cyclin-dependent kinases 4 and 6 (CDK4/6). PDB structure 5L2S (RCSB PDB, public domain). [View the structure at RCSB PDB](https://www.rcsb.org/structure/5L2S) · Drag to rotate · pinch to zoom 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 →](https://durgical.com/en/conditions/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 →](https://durgical.com/en/conditions/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 ### Serious (rare, important) - Severe diarrhoea with dehydration - Severe neutropenia and infection - Hepatotoxicity - Venous thromboembolism, including pulmonary embolism - Interstitial lung disease or pneumonitis ## 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. ## Memory aid «ABEmaciclib, Always Bring an antidiarrhoeal»: the CDK4/6 inhibitor of diarrhoea, and the only one that can go solo. ## 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. [Add to my cards (3)](https://durgical.app/estudiar/?add=/en/pharmacology/abemaciclib/) [More Pharmacology questions →](https://durgical.com/en/practice/?f=pharmacology) ## What the labels mean **High 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… ## Connections ## Related drugs 3 - [Palbociclib](https://durgical.com/en/pharmacology/palbociclib/) - [Ribociclib](https://durgical.com/en/pharmacology/ribociclib/) - [Tamoxifen](https://durgical.com/en/pharmacology/tamoxifen/) ## Related conditions 1 - [Breast cancer](https://durgical.com/en/conditions/breast-cancer/) [← Back to the class: CDK4/6 inhibitors](https://durgical.com/en/pharmacology/classes/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](https://medlineplus.gov/druginfo/meds/a617049.html) (MedlinePlus (U.S. National Library of Medicine), 2023); [Abemaciclib - NCI](https://www.cancer.gov/about-cancer/treatment/drugs/abemaciclib) (National Cancer Institute, 2024); [ATCDDD - ATC/DDD Index](https://atcddd.fhi.no/atc_ddd_index/?code=L01EF03) (WHO Collaborating Centre for Drug Statistics Methodology, 2026). ## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake Representative model, for educational purposes only. --- Source: https://durgical.com/en/pharmacology/abemaciclib/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/pharmacology/abemaciclib/