Skip to Accessibility Tools Skip to Content Skip to Footer

What is Ibrance® ? (palbociclib)

Ibrance is an oral targeted therapy that is a kinase inhibitor manufactured by Pfizer. Palbociclib is used to treat women and men with advanced or metastatic breast cancer that is hormone receptor positive and human epidermal growth factor receptor 2 (HER2) negative. It is used in combination with certain hormone therapies.1

What is the ingredient in Ibrance?

The active ingredient in Ibrance is palbociclib, a kinase inhibitor that targets cyclin dependent kinase (CDK) 4/6.1

How does palbociclib work?

Kinase inhibitors like palbociclib block certain proteins that control cellular functions like signaling, cell division, and survival. Palbociclib is a CDK 4/6 inhibitor. CDK4 and CDK6 are proteins that are important during a cell’s growth and replication cycles. In cancer cells, CDK4 and CDK6 may be overactive, which may cause the cancer cells to grow uncontrollably. By blocking CDK4/6, palbociclib can help slow the growth and division of breast cancer cells, but it may also interfere with the normal growth and division of healthy cells.1,2

Breast cancer cells that are hormone receptor-positive are stimulated by the presence of hormones like estrogen, which can increase the activity of CDK4/6. Palbociclib is used in combination with certain hormone therapies to block the growth of cancer cells in two ways: blocking the hormone receptors (hormone therapy) and blocking the enzymes CDK4/6 (palbociclib). In clinical trials, the combination of hormone therapy and palbociclib was more effective in slowing tumor growth than either of these treatments alone.1,3

What are some of the possible side effects of palbociclib?

Palbociclib may cause serious side effects, including lowering white blood cell counts. Because white blood cells are important for fighting infections, not having enough white blood cells can put you at risk for infections, some of which may potentially be life-threatening. People receiving palbociclib will have their blood tested to monitor their white blood cell count levels. If white blood cell counts become too low, treatment with palbociclib may be stopped or the dosage may be decreased.1

The most common side effects experienced by patients taking palbociclib in clinical trials included lowered white blood cell counts (neutropenia), infections, fatigue, nausea, inflammation of the mouth, anemia (lowered red blood cell counts), hair loss, diarrhea, lowered platelet levels, rash, vomiting, decreased appetite, weakness, and/or fever.1

There may be other possible side effects experienced with palbociclib. People taking palbociclib should talk to their doctor about any potential side effect that is bothersome or that persists.

Things to know about palbociclib

Because palbociclib can lower white blood cell levels, it should not be used in patients who already have lowered white blood cell counts. Levels of white blood cells should be checked prior to starting treatment with palbociclib and throughout treatment.1

People who are experiencing any signs of an infection (such as fever, chills, or other signs) should tell their doctor.1,3

Before starting treatment with palbociclib, patients should talk to their doctor about all their medications (prescription and over-the-counter), herbal supplements, and vitamins they are taking. Some medications or supplements may interfere with each other and may cause side effects.1,3

In addition, it should be noted that although it is rare, treatment with palbociclib can cause severe inflammation of the lungs. Patients should notify their health care professional right away if they have any new or worsening symptoms involving their lungs, as they may indicate a rare but life-threatening condition that can lead to death.4

Before starting treatment with palbociclib, patients should discuss with their doctor all their medical conditions, especially:

Palbociclib can cause harm to an unborn fetus and should not be used in pregnant women. Women who can become pregnant are advised to use effective contraception while taking palbociclib and for at least three weeks after stopping treatment with palbociclib. Men who are taking palbociclib and have female partners who can become pregnant should use effective contraception while taking palbociclib and for at least three months after stopping treatment with palbociclib.1,3

It is not known if palbociclib passes through breastmilk. Women should not breastfeed while taking palbociclib.1,3

Palbociclib may cause fertility problems in men, which could affect the ability to conceive a child.1,3

People taking palbociclib should not eat grapefruit or drink grapefruit juice, as grapefruit products may increase the levels of palbociclib in the body, which can increase the potential for side effects.1,3

Dosing information

Palbociclib should be taken in combination with hormone therapy. Palbociclib is taken orally with food. The recommended starting dose is 125 mg daily for 21 days, followed by 7 days off. The dosage may be reduced or stopped depending on the individual’s tolerability (how their body responds).1

Patients should take their medication as prescribed by their doctor. Patients should talk to their doctor if they have any questions, or if they have questions regarding their palbociclib regimen.

For more information, read the full prescribing information of palbociclib.

Written by: Editorial | Last reviewed: October 2019.
  1. Ibrance prescribing information. Pfizer Oncology. Available at http://labeling.pfizer.com/ShowLabeling.aspx?id=2191. Accessed 7/12/18.
  2. CDK4/6 inhibitors: where they are now and where they are headed in the future. ASCO Post. Available at http://www.ascopost.com/issues/may-10-2017-supplement-cdk46-inhibitors/cdk46-inhibitors-where-they-are-now-and-where-they-are-headed-in-the-future/. Accessed 7/12/18.
  3. Ibrance product website. Pfizer Oncology. Available at https://www.ibrance.com/how-ibrance-works. Accessed 7/12/18.
  4. US FDA. FDA warns about rare but severe lung inflammation with Ibrance, Kisqali, and Verzenio for breast cancer. Available at https://www.fda.gov/drugs/drug-safety-and-availability/fda-warns-about-rare-severe-lung-inflammation-ibrance-kisqali-and-verzenio-breast-cancer. Accessed 10/10/19.