Palbociclib is a kinase inhibitor indicated for the treatment of hormone receptor (HR)-positive, human epidermal growth factor receptor 2 (HER2)-negative advanced or metastatic breast cancer in combination with:
- An aromatase inhibitor as initial endocrine-based therapy in postmenopausal women; or
- Fulvestrant in women with disease progression following endocrine therapy.
Palbociclib is an inhibitor of Cyclin-dependent kinases (CDK) 4 and 6. cyclin D1 and CDK4/6 are downstream of signaling pathways that lead to cellular proliferation. Palbociclib reduced cellular proliferation of Estrogen receptor (ER)-positive breast cancer cell lines by blocking progression of the cell from G1 into s phase of the cell cycle. Treatment of breast cancer cell lines with the combination of Palboxen and antiestrogens leads to decreased retinoblastoma (RB) protein phosphorylation resulting in reduced E2F expression and signaling, and increased growth arrest compared to treatment with each drug alone. Treatment of ER-positive breast cancer cell lines with the combination of Palboxen and antiestrogens led to increased cell senescence compared to each drug alone, which was sustained for up to 6 days following Palboxen removal and was greater if antiestrogen treatment was continued. In vivo studies using a patient-derived ER-positive breast cancer xenograft model demonstrated that the combination of Palbociclib and letrozole increased the inhibition of RB phosphorylation, downstream signaling, and tumor growth compared to each drug alone.
Dosage & Administration
The recommended dose of Palboxen is a 125 mg capsule taken orally once daily for 21 consecutive days followed by 7 days off treatment to comprise a complete cycle of 28 days. Palbociclib should be taken with food. Patients should be encouraged to take their dose of Palbociclib at approximately the same time each day. For men treated with combination Palbociclib plus aromatase inhibitor therapy, consider treatment with an LHRH agonist according to current clinical practice standards.
Recommended Dose Modification for Adverse Reactions:
- Recommended Starting Dose: 125 mg/day
- First Dose Reduction: 100 mg/day
- Second Dose Reduction: 75 mg/day
If further dose reduction below 75 mg/day is required, discontinue. Or, as directed by the registered physician.
Use in Children: Palboxen is not indicated for use in children.
Palbociclib is primarily metabolized by CYP3A and Sulfotransferase (SULT) enzyme SULT2A1. Palbociclib is a
time-dependent inhibitor of CYP3A.
Agents That May Increase Palbociclib Plasma Concentrations: Effect of CYP3A-Inhibitors: Coadministration of a strong CYP3A inhibitor (Itraconazole) increased the plasma exposure of Palbociclib in patients by 87%. Avoid concomitant use of strong CYP3A inhibitors (e.g., Clarithromycin, Indinavir, Itraconazole, Ketoconazole, Lopinavir/Ritonavir, Nefazodone, Nelfinavir, Posaconazole, Ritonavir, Saquinavir, Telaprevir, Telithromycin, And Voriconazole). Avoid grapefruit or grapefruit juice during Palbociclib treatment. If coadministration of Palbociclib with a strong CYP3A inhibitor cannot be avoided, reduce the dose of Palbociclib.
Agents That May Decrease Palbociclib Plasma Concentrations: Effect of CYP3A Inducers: Coadministration of a strong CYP3A Inducer (Rifampin) decreased the plasma exposure of Palbociclib in healthy subjects by 85%. Avoid concomitant use of strong CYP3A inducers (E.G., Phenytoin, Rifampin, Carbamazepine, Enzalutamide, and St John’s Wort).
Drugs That May Have Their Plasma Concentrations Altered By Palbociclib: Coadministration of Midazolam with multiple doses of Palbociclib increased the Midazolam plasma exposure by 61%, in patients, compared to administration of Midazolam alone. The dose of the sensitive CYP3A substrate with a narrow therapeutic index (e.g., Alfentanil, Cyclosporine, Dihydroergotamine, Ergotamine, Everolimus, Fentanyl, Pimozide, Quinidine, Sirolimus, And Tacrolimus) may need to be reduced, as Palbociclib may increase its exposure.
Common side effects of Palbociclib include: WBC decreased, Neutrophils decreased, Neutropenia, Platelets decreased, infections, AST increased, ALT increased, Leukopenia, Fatigue, Nausea, Hair loss, Inflammation of the mouth and lips, Diarrhea, Anemia, Rash, Weakness/lethargy, Vomiting, Thrombocytopenia, Dry skin, Fever.
Pregnancy & Lactation
Palbociclib can cause fetal harm when administered to a pregnant woman. Advise pregnant women of the potential risk to a fetus. Risk of major birth defects and miscarriage in clinically recognized pregnancies is 2%-4% and 15%-20%, respectively.
Precautions & Warnings
Neutropenia: Neutropenia was the most frequently reported adverse reaction in Study 1 (PALOMA-2) with an incidence of 80% and Study 2 (PALOMA-3) with an incidence of 83%. A Grade 3 in neutrophil counts was reported in 66% of patients receiving Palbociclib plus letrozole in Study 1 and 66% of patients receiving Palcigen plus fulvestrant in Study In Study 1 and 2, the median time to first episode of any grade neutropenia was 15 days and the median duration of Grade 3 was 7 days. Monitor complete blood counts prior to Palbociclib therapy and at the beginning of each cycle, well as on Day 15 of the 2 cycles, and as clinically dose. Dose or delay in treatment cycles recommended for patients who develop Grade 3 or 4 neutropenia. Febrile neutropenia has been reported in 1.8% of patients exposed to Palbociclib Studies 1 and 2. One death due to neutropenia was observed in Study Physicians should inform patients to promptly report any of fever.
Interstitial Lung Disease (ILD)/Pneumonitis: Severe, life-threatening, fatal interstitial lung disease (ILD) and/or pneumonitis can occur in treated with cyclin-dependent kinase 4/6 (CDK4/6) inhibitors, including Palbociclib when taken in combination with endocrine therapy. Across clinical trials (PALOMA-1, PALOMA-2, PALOMA-3), 1.0% of Palbociclib treated patients had ILD/pneumonitis of any grade, 0.1 % had Grade 3 or 4 and no fatal cases were reported. Additional cases of ILD/pneumonitis have been observed in the postmarketing setting, with fatalities reported. Monitor patients for pulmonary symptoms indicative of ILD/pneumonitis hypoxia, cough, In patients who have new or symptoms and suspected to have developed interrupt Palboxen immediately and evaluate the Permanently discontinue Palboxen in patients with severe ILD or pneumonitis.
Embryo Fetal Toxicity: Based on findings from animal studies and its mechanism of action, Palbociclib can cause fetal harm when administered to a pregnant woman. In animal reproduction studies administration of Palboxen to pregnant and during resulted in embryo-fetal toxicity at maternal that were 4 times the human clinical exposure based on area under the (AUC). Advise pregnant women of the potential risk to a Advise females of reproductive potential to use effective contraception during treatment with Palbociclib and for at least 3 weeks after the last dose.
There is no known antidote for Palbociclib. The treatment of overdose of Palbociclib should consist of general supportive measures.
Protein kinase inhibitor
Keep below 30°C temperature, away from light & moisture. Keep out of the reach of children.
Manufacturer: Everest Pharmaceuticals Ltd.
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