Palbociclib

Pronunciation: pal-boe-SYE-klib.

Generic name
palbociclib
Drug class
Cyclin-dependent kinase 4/6 (CDK4/6) inhibitor; antineoplastic agent
Form
Tablet or capsule (75 mg, 100 mg, 125 mg)
Route
Oral
Legal status
Prescription-only; oncologist-managed

Availability and supply rules vary by country

Trade names by country: United States · United Kingdom · Canada · Australia · New Zealand

Australia: Ibrance (4) · Full directory

What palbociclib is and how it works

Palbociclib is a prescription-only oral cancer medicine (a CDK4/6 inhibitor) used to treat hormone receptor (HR)-positive, HER2-negative advanced or metastatic breast cancer, given in combination with hormone (endocrine) therapy such as an aromatase inhibitor or fulvestrant. (1) (3)

You take palbociclib once a day for 21 days, then have a 7-day break, repeating this 28-day cycle alongside your hormone therapy. It should only be prescribed and managed by a doctor experienced in cancer treatment, because it requires regular blood tests to check for a drop in white blood cells (neutropenia), and carries other serious risks including lung inflammation and effects on an unborn baby.

Mechanism of action: how palbociclib works

Palbociclib is a reversible, selective, small-molecule inhibitor of cyclin-dependent kinases 4 and 6 (CDK4/6), which are involved in the cell cycle. By inhibiting CDK4/6, palbociclib blocks the phosphorylation of the retinoblastoma protein, arresting the cell cycle and reducing proliferation of hormone-receptor-positive breast cancer cells, particularly when combined with hormone (endocrine) therapy. (1) (2)

What palbociclib is used for

HR-positive, HER2-negative advanced or metastatic breast cancer

Used in combination with an aromatase inhibitor as initial hormone-based therapy, or with fulvestrant after the disease has progressed on prior hormone therapy, in women (pre/perimenopausal or postmenopausal) or men. (1) (2) (3)

PIK3CA-mutated, endocrine-resistant breast cancer (United States)

Per a 2025 US label update, also used in combination with inavolisib and fulvestrant for endocrine-resistant, PIK3CA-mutated, HR-positive, HER2-negative disease detected by an FDA-approved test, following recurrence on or after completing adjuvant endocrine therapy. This is a recently added, more specific use, not a long-established indication. (1)

HER2-positive metastatic breast cancer maintenance (United States)

Per a real, very recent (2026) US approval, also used in combination with trastuzumab, with or without pertuzumab, and endocrine therapy for the maintenance treatment of HR-positive, HER2-positive metastatic breast cancer following induction treatment. (1)

Before taking palbociclib

Do not take / not appropriate for

  • Do not take palbociclib if you have had an allergic reaction to it or any of its ingredients. (all confirmed markets) (1) (3)
  • Do not take St John's Wort while on palbociclib -- this combination is contraindicated because it can reduce palbociclib levels. (United Kingdom) (2)

Tell your clinician about

  • Any history of low blood counts, infections, or bleeding problems.
  • Any history of lung disease or breathing problems.
  • Any personal or family history of blood clots (deep vein thrombosis or pulmonary embolism).
  • All other medicines you take, especially strong CYP3A inhibitors or inducers, or St John's Wort.
  • Pregnancy, plans for pregnancy, or breastfeeding -- and whether effective contraception is in place, since palbociclib can cause fetal harm.
  • Whether you or your partner may wish to preserve fertility, since male fertility may be affected.
(1) (2)

How to take palbociclib

  • Take palbociclib once daily, with or without food, at approximately the same time each day.
  • Swallow tablets/capsules whole -- do not chew, crush, or split them, and do not take a tablet/capsule that is broken, cracked, or otherwise not intact.
  • Take palbociclib for 21 consecutive days, then take a 7-day break -- this 28-day pattern is one treatment cycle, repeated as directed.
  • If you vomit or miss a dose, do not take an extra dose -- take your next dose at the usual scheduled time.
  • You will have regular blood tests, particularly at the start of treatment and each new cycle, to check for a drop in white blood cells.
  • Do not change your dose or stop taking palbociclib without talking to your oncology team first.
(1) (3)

Procedures and treatment changes

Tell the treating team before surgery, procedures, or any medicine change. Do not alter treatment without the responsible clinician. (1) (2) (3) (4) (5) (6)

Missed dose

If you vomit after taking a dose, or miss a dose entirely, do not take an additional or replacement dose -- simply take your next dose at the regular scheduled time.

Overdose

Seek urgent medical attention if too much palbociclib may have been taken, or if you develop signs of a severe drop in blood counts (fever, unusual bruising or bleeding) or breathing difficulty. (3)

Side effects

Side effects and their urgency vary; report severe, persistent, or concerning symptoms.

Low white blood cell counts (neutropenia) -- very common, occurring in the large majority of patients.

What to notice: Low white blood cell counts (neutropenia) -- very common, occurring in the large majority of patients.

What to do: Discuss persistent or troublesome symptoms with the treating clinician or pharmacist. (2)

Infections -- very common.

What to notice: Infections -- very common.

What to do: Discuss persistent or troublesome symptoms with the treating clinician or pharmacist. (2)

Fatigue, nausea, mouth sores (stomatitis), diarrhoea, hair loss (alopecia) -- very common.

What to notice: Fatigue, nausea, mouth sores (stomatitis), diarrhoea, hair loss (alopecia) -- very common.

What to do: Discuss persistent or troublesome symptoms with the treating clinician or pharmacist. (2)

Low platelet counts (thrombocytopenia) and low red blood cell counts (anaemia) -- very common.

What to notice: Low platelet counts (thrombocytopenia) and low red blood cell counts (anaemia) -- very common.

What to do: Discuss persistent or troublesome symptoms with the treating clinician or pharmacist. (2)

Changes in liver blood tests (AST/ALT increased) and blood creatinine increased -- common.

What to notice: Changes in liver blood tests (AST/ALT increased) and blood creatinine increased -- common.

What to do: Discuss persistent or troublesome symptoms with the treating clinician or pharmacist. (1)

Serious warnings

Neutropenia (low white blood cell count) — high caution

Symptoms: Fever, chills, sore throat, or other signs of infection.

Action: Your care team monitors your complete blood count before treatment starts, at the beginning of every cycle, and on day 15 of your first two cycles, then periodically after that. Your dose may be withheld or reduced based on the severity (grade) of any drop, and febrile neutropenia (a drop in white cells with fever) requires prompt medical attention -- report any fever immediately. In Canada, this is presented as a formal 'Serious Warnings and Precautions' box, the most prominent safety designation Health Canada uses; the US and UK labels present the same substance as a detailed Warnings and Precautions section rather than a boxed warning. (1) (2) (3)

Signs of interstitial lung disease or pneumonitis (lung inflammation) — emergency

Symptoms: New or worsening shortness of breath, cough, or low oxygen levels.

Action: Contact your care team immediately -- severe and fatal cases have been reported. Treatment is interrupted right away if this is suspected, and permanently stopped if a severe case is confirmed. (1) (2)

Signs of a blood clot (venous thromboembolism) — high caution

Symptoms: Swelling, pain, or redness in a leg; sudden shortness of breath or chest pain.

Action: Seek medical attention promptly -- blood clots (including deep vein thrombosis and pulmonary embolism) have been reported more often in patients treated with palbociclib than with hormone therapy alone. (3)

Risk to an unborn baby — high caution

Symptoms: Not applicable -- this is a treatment-related risk, not a symptom to watch for.

Action: Palbociclib can cause fetal harm and is not recommended during pregnancy. Women who could become pregnant, and their partners, must use a highly effective method of contraception during treatment and for a defined period afterward (3 weeks for women, 14 weeks for men, per the UK label). (1) (2)

Signs of infection — moderate caution

Symptoms: Fever, chills, cough, or other new signs of infection.

Action: Contact your care team promptly -- serious (Grade 3-4) infections have been reported in a meaningful proportion of patients, related to the drop in white blood cells this medicine can cause. (2) (3)

Interactions

  • Strong CYP3A inhibitors (such as clarithromycin, itraconazole, ritonavir, ketoconazole, or grapefruit/grapefruit juice) should be avoided; if unavoidable, your dose will be reduced. (1) (3)
  • Strong CYP3A inducers (such as rifampin, carbamazepine, or phenytoin) should be avoided, as they can reduce palbociclib's effectiveness. (1)
  • St John's Wort must not be combined with palbociclib. (2)
  • Sensitive CYP3A substrate medicines with a narrow safety margin may need their own dose reduced when combined with palbociclib. (1)

Pregnancy, breastfeeding, kidney/liver function, age

Pregnancy

Palbociclib can cause fetal harm and is not recommended during pregnancy. Effective contraception is required during treatment and for a period afterward (3 weeks for women, 14 weeks for men, per the UK label). (1) (2) (3) (4) (5) (6)

Breastfeeding

It is unknown whether palbociclib passes into human breast milk. Breastfeeding is advised against during treatment because of the potential for serious adverse reactions in a nursing infant. (1) (2) (3) (4) (5) (6)

Children

Safety and efficacy in children have not been established, and Health Canada has not authorised a pediatric indication. (1) (2) (3) (4) (5) (6)

Elderly

No overall differences in safety or efficacy were seen between patients 65 and older and younger patients in the main clinical trials, although anaemia was reported more frequently in older patients treated with palbociclib plus letrozole specifically. (1) (2) (3) (4) (5) (6)

Hepatic_impairment

Severe hepatic impairment: reduce dose to 75 mg once daily. No adjustment needed for mild-to-moderate impairment. (1) (2) (3) (4) (5) (6)

Renal_impairment

No dose adjustment needed for creatinine clearance of 15 mL/min or greater. (1) (2) (3) (4) (5) (6)

Fertility

Male fertility may be compromised by palbociclib treatment; sperm preservation before starting treatment may be considered. (1) (2) (3) (4) (5) (6)

Source_ids

US-FDA-IBRANCE-2025,UK-EMC-IBRANCE-125MG-2026,CA-HEALTHCANADA-IBRANCE-2024 (1) (2) (3) (4) (5) (6)

Monitoring

Before starting

  • Baseline complete blood count
  • Baseline liver and kidney function
  • Pregnancy test and contraception plan where relevant
  • Review of all other medicines for CYP3A interactions

During treatment

  • Complete blood count before each new cycle and on Day 15 of the first two cycles, then periodically.
  • Monitoring for new respiratory symptoms (possible ILD/pneumonitis).
  • Monitoring for signs of infection or fever.
  • Monitoring for signs of blood clots.
  • Ongoing contraception during treatment and for the required period afterward.
(1) (2) (3)

Storage

Store at room temperature, away from moisture and light, out of reach of children.

Professional information

Clinician-facing context only, sourced from the current US, UK, and Canadian labels; verify against the current full label before prescribing. Should only be prescribed and managed by a clinician experienced in the use of anti-cancer agents.

United States / United Kingdom / Canada / Australia / New Zealand / European Union

Indication: HR-positive, HER2-negative advanced/metastatic breast cancer, with an aromatase inhibitor or fulvestrant; (US, 2025 update) with inavolisib and fulvestrant for PIK3CA-mutated disease; (US, 2026 approval) with trastuzumab +/- pertuzumab for HER2-positive maintenance

Dose summary: 125 mg once daily x 21 days, 7 days off (28-day cycle); dose reductions to 100 mg then 75 mg for toxicity, with treatment withdrawal recommended if a reduction below 75 mg would otherwise be needed; severe hepatic impairment or strong CYP3A inhibitor: 75 mg once daily.

Renal context: No adjustment needed for CrCl >=15 mL/min. (1) (2) (3)

Mechanism of action

Hepatic guidance

Severe hepatic impairment requires dose reduction to 75 mg once daily.

Overdose note

Manage supportively; monitor blood counts and general toxicity closely. (1) (2)

Frequently asked questions

Does palbociclib carry a boxed warning?

It depends on the country. The current US label explicitly states 'Contraindications: None' and has no boxed warning -- neutropenia, interstitial lung disease/pneumonitis, and embryo-fetal toxicity are presented as detailed Warnings and Precautions instead. The UK label follows the same non-boxed approach. Health Canada's product monograph, however, does carry a formal 'Serious Warnings and Precautions' box, specifically naming neutropenia as the significant adverse drug reaction identified in clinical trials -- this is a real, Canada-specific difference in how the same underlying risk is regulatory-formatted. (1) (3)

Why do I need frequent blood tests on palbociclib?

Palbociclib very commonly causes neutropenia (a drop in a type of white blood cell that fights infection), affecting the large majority of patients in clinical trials. Your care team checks your complete blood count before starting treatment, at the beginning of every 28-day cycle, and on day 15 of your first two cycles, adjusting your dose if needed based on how low your counts fall. (2)

Can palbociclib affect an unborn baby?

Yes -- palbociclib can cause fetal harm and is not recommended during pregnancy. Effective contraception is required during treatment and for a period afterward (3 weeks for women and 14 weeks for men, per the UK label), and male fertility may also be affected, so sperm preservation may be worth discussing before starting treatment. (1) (2)

Is palbociclib used for anything besides the standard aromatase-inhibitor or fulvestrant combination?

Yes, in the United States there are newer, more specific combination uses: with inavolisib and fulvestrant for a genetically defined (PIK3CA-mutated) form of endocrine-resistant breast cancer (added to the label in 2025), and, per a very recent 2026 approval, with trastuzumab (with or without pertuzumab) for maintenance treatment of HER2-positive metastatic breast cancer. These are newer, more specific uses rather than the original, longer-established indication. (1)

What is the mechanism of action of palbociclib?

Palbociclib is a reversible, selective, small-molecule inhibitor of cyclin-dependent kinases 4 and 6 (CDK4/6), which are involved in the cell cycle. By inhibiting CDK4/6, palbociclib blocks the phosphorylation of the retinoblastoma protein, arresting the cell cycle and reducing proliferation of hormone-receptor-positive breast cancer cells, particularly when combined with hormone (endocrine) therapy. (1) (2)

What is the generic name of Palbociclib?

The generic name is palbociclib. (1) (2)

What class of drug is palbociclib?

Palbociclib is classed as: Cyclin-dependent kinase 4/6 (CDK4/6) inhibitor; antineoplastic agent. (1) (2)

References

  1. IBRANCE (palbociclib) tablets, for oral use -- full prescribing information (revised 04/2025, accessdata document 212436s008lbl.pdf)U.S. Food and Drug Administration, accessdata.fda.gov full prescribing information · United States · accessed 2026-07-30 · source 1
  2. IBRANCE 125 mg film-coated tablets -- Summary of Product Characteristics (product 11962)UK Medicines and Healthcare products Regulatory Agency / electronic medicines compendium (emc), Summary of Product Characteristics · United Kingdom · accessed 2026-07-30 · source 2
  3. IBRANCE (Palbociclib) capsules/tablets, 75/100/125 mg -- Product Monograph, revised 4 September 2024Health Canada -- Pfizer Canada ULC, product monograph · Canada · accessed 2026-07-30 · source 3
  4. IBRANCE (palbociclib) capsules and tablets, 75/100/125 mg -- ARTG registrationsAustralian Therapeutic Goods Administration (TGA), Australian Register of Therapeutic Goods (ARTG) · Australia · accessed 2026-07-30 · source 4
  5. IBRANCE (palbociclib) 75 mg capsules -- New Zealand Data SheetNew Zealand Medicines and Medical Devices Safety Authority (Medsafe); Pharmac (funding authority) · New Zealand · accessed 2026-07-30 · source 5
  6. Ibrance (palbociclib) -- European Public Assessment Report (EPAR), EU marketing authorisation, authorised since 9 November 2016European Medicines Agency (EMA) · European Union · accessed 2026-07-30 · source 6

Brand names by country

Single-ingredient palbociclib names are shown separately by country. Product availability, strengths, and supply rules can change; combination products are not included here.

Priority countries

United States

  • Ibrance75 mg, 100 mg, 125 mg · pfizer laboratories div pfizer inc

United Kingdom

  • Ibrance (2)UK licensed · 75 mg, 100 mg, 125 mg · Pfizer

Canada

  • IBRANCE

Australia

  • Ibrance (4)TGA ARTG registered · 75 mg, 100 mg, 125 mg · Pfizer Australia Pty Ltd

New Zealand

  • Ibrance (5)Medsafe authorised Pharmac funded · 75 mg · Pfizer (Pharmac-funded since 1 April 2020)
View brands in additional countries.

European Union

Ibrance; Palbociclib Viatris (generic) (6)

This page provides general reference information about palbociclib and is not a substitute for advice from the oncology team managing your treatment. All dosing, monitoring, and contraception decisions should be made with your treating specialist.

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