Ibrance (Palbociclib)

Ibrance is a CDK4/6 inhibitor used in the management of hormone‑driven breast cancer.

• Hormone receptor‑positive, HER2‑negative advanced breast cancer: delays disease progression when combined with endocrine therapy.
• Hormone receptor‑positive, HER2‑negative metastatic breast cancer: extends progression‑free survival in patients receiving standard hormonal treatment.
• Combination with endocrine therapy: enhances the effectiveness of hormonal agents in controlling tumor growth.

• Palbociclib selectively inhibits cyclin‑dependent kinases 4 and 6, which are essential for phosphorylation of the retinoblastoma protein and transition from the G1 to S phase of the cell cycle. By blocking CDK4/6 activity, the drug induces G1‑phase arrest in tumor cells, thereby suppressing cellular proliferation in hormone‑responsive breast cancer.

Common Side Effects

• Neutropenia: reduced neutrophil count, increasing infection risk.
• Leukopenia: lowered white blood cell count.
• Anemia: decreased red blood cells causing fatigue.
• Fatigue: general tiredness and reduced stamina.
• Nausea: upset stomach and urge to vomit.
• Diarrhea: loose, frequent stools.

Serious or Rare Side Effects

• Febrile neutropenia: fever with low neutrophils, requiring urgent care.
• Pulmonary embolism: blood clot in the lungs, a medical emergency.
• Severe infections: opportunistic infections due to immune suppression.
• Elevated liver enzymes: potential liver injury indicated by increased ALT/AST.
• QT interval prolongation: heart rhythm disturbance that may lead to arrhythmia.

Before initiating therapy, patients should be evaluated for blood‑cell counts and liver function, and monitored regularly throughout treatment.

• Monitor blood counts: perform complete blood count (CBC) before each cycle.
• Assess liver function: check ALT/AST levels periodically.
• Evaluate infection risk: advise patients to report fever or signs of infection promptly.
• Avoid strong CYP3A4 inhibitors: drugs such as ketoconazole may increase palbociclib exposure.
• Counsel on pregnancy: use effective contraception; safety in pregnancy is not established.
• Store at room temperature: keep tablets in the original container, protect from moisture and direct sunlight.

Palbociclib may interact with medicines that affect its metabolism or absorption.

Major Interactions (Avoid)

• Strong CYP3A4 inhibitors (e.g., ketoconazole, clarithromycin): can raise palbociclib plasma levels.
• Potent CYP3A4 inducers (e.g., rifampin, carbamazepine): may reduce efficacy by lowering drug concentrations.

Moderate Interactions (Monitor Closely)

• Moderate CYP3A4 inhibitors (e.g., fluconazole, diltiazem): may modestly increase exposure.
• Antacids containing aluminum or magnesium: can affect gastrointestinal absorption; separate dosing by at least 2 hours.
• Warfarin: monitor INR as palbociclib may alter anticoagulant effect.