Ribociclib

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, early or advanced, with hormone therapy. It prolongs QT: ECG and electrolytes.

Updated Nov 1, 2026

Also called: ribociclib succinate

Quick facts

Group: CDK4/6 inhibitors
Target: Cyclin-dependent kinases 4 and 6 (CDK4/6)
Used for: HR-positive · HR-positive
Key effects: Neutropenia and leukopenia · Nausea · Hair loss
Monitor: ECG and electrolytes before starting · Liver tests
ATC: L01EF02

No doses: the clinician sets them by the current guideline.

Mechanism of action

Cyclin-dependent kinases 4 and 6 (CDK4/6)Ribociclib

The figure shows ribociclib in the ATP pocket of human CDK6.

Target in 3D: Cyclin-dependent kinases 4 and 6 (CDK4/6). PDB structure 5L2T (RCSB PDB, public domain). View the structure at RCSB PDB

Like palbociclib, ribociclib blocks the ATP site of CDK4 and CDK6, keeps Rb unphosphorylated and arrests hormone-dependent breast cancer cells in G1. It is given with an aromatase inhibitor or fulvestrant. Unlike palbociclib, it lengthens the QT interval in a concentration-dependent way.

Blocks the ATP site of CDK4 and CDK6
Rb stays active: cells arrest in G1
Given with an aromatase inhibitor or fulvestrant

Indications

HR-positive, HER2-negative stage II or III early breast cancer at high risk of recurrence, with an aromatase inhibitor. Breast cancer →
HR-positive, HER2-negative advanced or metastatic breast cancer, with an aromatase inhibitor or with fulvestrant. Breast cancer →

Adverse effects

Common

Neutropenia and leukopenia
Nausea, vomiting, diarrhoea or constipation
Fatigue and headache
Hair loss, itching, rash
Cough, back pain, swelling of the legs

Contraindications

Avoided or used with great caution with long QT, slow or irregular heartbeat, or uncorrected low potassium, calcium, phosphorus or magnesium

Key interactions

Other QT-prolonging drugs (some antiarrhythmics, macrolides, antipsychotics): Additive risk of QT prolongation and arrhythmia.
Strong CYP3A4 inhibitors (clarithromycin, itraconazole, ketoconazole, ritonavir) and grapefruit: Raise its levels and its toxicity.
Strong CYP3A4 inducers (rifampicin, carbamazepine, phenytoin, St John's wort): Lower its levels and can make it fail.

What is monitored

ECG and electrolytes before starting and during treatment
Complete blood count before starting and regularly
Liver tests
Lung symptoms and skin

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.
If the patient vomits after a dose, the dose is not repeated; the next one is taken at the usual time.

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

Check that a baseline ECG and electrolytes are on file before the first dose.
Review the medication list for other QT-prolonging drugs.
Teach to report palpitations, fainting, fever, blistering rash or jaundice.
Confirm a negative pregnancy test before the first dose and teach contraception during treatment and afterwards.

Pharmacokinetics

Absorption: Oral tablets, with or without food, once daily in cycles.
Metabolism: Liver, CYP3A.
Half-life: Roughly 30 to 55 hours.

Test yourself

Think of the answer, then tap the question to see it.

Which test is required before and during ribociclib, unlike palbociclib?

An ECG with electrolytes, because ribociclib prolongs the QT interval.

Which two serious non-haematological toxicities of ribociclib are classic exam answers?

Pneumonitis or interstitial lung disease, and severe skin reactions such as Stevens-Johnson syndrome (also hepatotoxicity).

In which early breast cancer setting is ribociclib used?

Stage II or III HR-positive, HER2-negative disease at high risk of recurrence, with an aromatase inhibitor.

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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: Ribociclib: MedlinePlus Drug Information (MedlinePlus (U.S. National Library of Medicine), 2025); Ribociclib Succinate - 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.