[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/) › Ribociclib

# 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](https://durgical.com/en/pharmacology/classes/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.

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)**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](https://www.rcsb.org/structure/5L2T) · Drag to rotate · pinch to zoom

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 →](https://durgical.com/en/conditions/breast-cancer/)
- HR-positive, HER2-negative advanced or metastatic breast cancer, with an aromatase inhibitor or with fulvestrant. [Breast cancer →](https://durgical.com/en/conditions/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

### Serious (rare, important)

- QT prolongation and arrhythmia
- Interstitial lung disease or pneumonitis
- Severe skin reactions (Stevens-Johnson syndrome, toxic epidermal necrolysis)
- Severe neutropenia and infection
- Hepatotoxicity

## 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.

## Memory aid

«RIBOciclib keeps Rhythm in mind»: the CDK4/6 inhibitor that needs an ECG.

## 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.

[Add to my cards (3)](https://durgical.app/estudiar/?add=/en/pharmacology/ribociclib/)

[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/)
- [Abemaciclib](https://durgical.com/en/pharmacology/abemaciclib/)
- [Letrozole](https://durgical.com/en/pharmacology/letrozole/)

## 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: [Ribociclib: MedlinePlus Drug Information](https://medlineplus.gov/druginfo/meds/a617008.html) (MedlinePlus (U.S. National Library of Medicine), 2025); [Ribociclib Succinate - NCI](https://www.cancer.gov/about-cancer/treatment/drugs/ribociclib) (National Cancer Institute, 2024); [ATCDDD - ATC/DDD Index](https://atcddd.fhi.no/atc_ddd_index/?code=L01EF02) (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.

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License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/pharmacology/ribociclib/