Abemaciclib is an oral targeted medicine used to treat hormone receptor-positive, HER2-negative breast cancer. It belongs to a class of medicines called CDK4/6 inhibitors, and unlike some other medicines in this class, it's taken continuously without a scheduled break. It is a prescription-only medicine.

• Therapeutic Class: Anti-cancer (oncology) targeted therapy for breast cancer.

• Pharmacological Class: Cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitor.

• Drug Family: Small-molecule CDK4/6-targeted therapies.

• ATC Classification: L01EF03 (Abemaciclib).

Approved: Hormone receptor-positive (HR+), HER2-negative breast cancer — as adjuvant treatment with endocrine therapy for high-risk, node-positive early breast cancer; combined with an aromatase inhibitor as initial therapy for advanced or metastatic disease; combined with fulvestrant after disease progression on endocrine therapy; and as monotherapy after progression on endocrine therapy and prior chemotherapy in the metastatic setting.

Commonly used for: Women (and eligible men) with HR+/HER2- breast cancer at high risk of recurrence, or with advanced/metastatic disease, as part of a broader hormone-based treatment strategy.

Off-label use (only under medical guidance): Being studied in other hormone-driven cancers in clinical trials; not routine outside its approved breast cancer indications.

● Oral tablets: 50 mg, 100 mg, 150 mg, and 200 mg.

Abemaciclib blocks two enzymes, CDK4 and CDK6, that cancer cells need to progress through the cell division cycle. By inhibiting these enzymes, abemaciclib stops hormone receptor-positive breast cancer cells from dividing and growing, working alongside hormone-based therapies that reduce the cancer's fuel supply (estrogen).

• Standard dose: 150 mg taken orally twice daily, continuously (without a scheduled treatment break), typically at approximately the same time each day (e.g., 8:00 AM and 8:00 PM), with or without food.

• Condition-wise dose: As monotherapy (without a combination partner), the dose is 200 mg twice daily; reduce to 100 mg or 50 mg twice daily for significant diarrhoea or blood count changes.

• Route: Oral; tablets should be swallowed whole and not chewed, crushed, or split.

• Missed dose: If a dose is missed or vomiting occurs, do not take an additional dose — take the next scheduled dose as usual.

• Overdose: May worsen known side effects such as severe diarrhoea or low blood counts; requires medical attention.

• Common: Diarrhoea (very common, occurring in the large majority of patients), nausea, fatigue, decreased appetite, and low blood counts.

• Serious: Severe diarrhoea with dehydration and risk of infection, venous thromboembolism (blood clots), and interstitial lung disease (rare but serious lung inflammation).

• Emergency symptoms: Severe or persistent diarrhoea (more than 2 bowel movements above baseline in a day), leg swelling or pain, sudden shortness of breath or chest pain, or signs of serious infection.

• Recovery advice: Diarrhoea is one of the most common side effects, often starting within the first week or month of treatment; standard guidance is to start an anti-diarrhoeal medicine (such as loperamide) at the first sign of loose stools, along with increased fluid intake.

• Pregnancy: Can cause fetal harm; effective contraception is required during treatment and for 3 weeks after the last dose.

• Breastfeeding: Not recommended during treatment and for a period after the last dose.

• Liver disease: No dose adjustment needed in mild to moderate impairment; dosing frequency is reduced to once daily in severe impairment (Child-Pugh C).

• Kidney disease: Used with monitoring; increases in serum creatinine have been observed, which may not reflect true kidney function decline.

• Elderly: Commonly used in this age group; monitored for tolerability, particularly diarrhoea and blood count changes.

• Children: Not approved for use in children.

● Strong CYP3A4 inhibitors (e.g., ketoconazole): significantly increase abemaciclib levels; avoided if possible, or the abemaciclib dose reduced (e.g., to 100 mg or 50 mg twice daily) if combined use is unavoidable.

● Strong CYP3A4 inducers (e.g., rifampin): can significantly reduce abemaciclib effectiveness.

● Other myelosuppressive drugs: may increase the risk of low blood counts when combined.

● Anticoagulants: monitored more closely given abemaciclib's own associated risk of blood clots (venous thromboembolism).

● Complete blood counts before starting and periodically during treatment.

● Liver function tests periodically.

● Assessment of diarrhoea frequency/severity at each visit.

● Monitoring for signs of blood clots (leg swelling, shortness of breath) throughout treatment.

Palbociclib, Ribociclib (other CDK4/6 inhibitors, dosed on a 21-days-on/7-days-off schedule rather than continuously).

Used with endocrine therapy (tamoxifen or an aromatase inhibitor) for early breast cancer; combined with an aromatase inhibitor or fulvestrant for advanced/metastatic disease; can also be used as monotherapy at a higher dose after prior endocrine therapy and chemotherapy.

● Breast Cancer Medicines

● CDK4/6 Inhibitors

● Hormone Receptor-Positive Cancer Therapies

1. Breast Cancer Advanced Treatment

2. Chemotherapy and Pregnancy: What Should You Keep in Mind?

1. https://verzenio.lilly.com/hcp/moa

2. https://www.drugs.com/abemaciclib.html

The information on this page is for educational purposes only and is not a substitute for medical advice. Please consult your oncologist to know if this treatment is appropriate for your condition.