Abemaciclib is a kinase inhibitor used in the treatment of breast cancer under different clinical settings:

• In combination with endocrine therapy (such as tamoxifen or an aromatase inhibitor) for adjuvant treatment of adult patients with hormone receptor (HR)-positive, HER2-negative, node-positive early breast cancer who are at high risk of recurrence and have a Ki-67 score ≥20%.
• In combination with an aromatase inhibitor as initial endocrine-based therapy for postmenopausal women and men with HR-positive, HER2-negative advanced or metastatic breast cancer.
• In combination with fulvestrant for adult patients with HR-positive, HER2-negative advanced or metastatic breast cancer whose disease has progressed after endocrine therapy.
• As a single-agent therapy for adult patients with HR-positive, HER2-negative advanced or metastatic breast cancer who have experienced disease progression following endocrine therapy and prior chemotherapy.

Abemaciclib is a selective inhibitor of cyclin-dependent kinases 4 and 6 (CDK4 and CDK6), which play a critical role in regulating the cell cycle. In hormone receptor-positive breast cancer, activation of CDK4/6 leads to phosphorylation of the retinoblastoma (Rb) protein, promoting cell cycle progression and tumor cell proliferation. Abemaciclib works by inhibiting this phosphorylation process, thereby blocking the transition of cells from the G1 phase to the S phase. This results in cell cycle arrest, cellular aging (senescence), and programmed cell death (apoptosis).

Preclinical studies have shown that continuous administration of abemaciclib, either alone or combined with anti-estrogen therapies, can significantly reduce tumor growth.

Abemaciclib tablets are taken orally with or without food.

• Recommended starting dose in combination with fulvestrant, tamoxifen, or an aromatase inhibitor: 150 mg twice daily.
• Recommended starting dose as monotherapy: 200 mg twice daily.
• Dosing interruption and/or dose reductions may be required based on individual safety and tolerability

CYP3A Inhibitors: Concomitant use with ketoconazole should be avoided. When used with other strong or moderate CYP3A inhibitors, the dose of Abemaciclib should be reduced.

CYP3A Inducers: Avoid using Abemaciclib together with strong or moderate CYP3A inducers, as they may reduce its effectiveness.

Common adverse effects (≥20%) include. Diarrhea, Neutropenia, Nausea, Abdominal pain, Infections, Fatigue, Anemia, Leukopenia, Loss of appetite, Vomiting, Headache, Hair loss (alopecia).

Diarrhea: Abemaciclib can cause severe cases of diarrhea, associated with dehydration and infection. Instruct patients at the first sign of loose stools to initiate antidiarrheal therapy, increase oral fluids, and notify their healthcare provider.

Neutropenia: Monitor complete blood counts prior to the start of Abemaciclib therapy, every 2 weeks for the first 2 months, monthly for the next 2 months, and as clinically indicated.

Interstitial Lung Disease (ILD)/Pneumonitis: Severe and fatal cases of ILD/pneumonitis have been reported. Monitor for clinical symptoms or radiological changes indicative of ILD/pneumonitis. Permanently discontinue Abemaciclib in all patients with Grade 3 or 4 ILD or pneumonitis.

Hepatotoxicity: Increases in serum transaminase levels have been observed. Perform liver function tests (LFTs) before initiating treatment with Abemaciclib. Monitor LFTs every two weeks for the first two months, monthly for the next two months, and as clinically indicated.

Venous Thromboembolism: Monitor patients for signs and symptoms of thrombosis and pulmonary embolism and treat as medically appropriate.

Embryo-Fetal Toxicity: Can cause fetal harm. Advise patients of the potential risk.

Diarrhea: Severe diarrhea may occur, sometimes leading to dehydration or infection. Patients should begin antidiarrheal treatment early, increase fluid intake, and inform their doctor promptly.

Neutropenia: Monitor complete blood counts before starting treatment, every 2 weeks for the first 2 months, monthly for the next 2 months, and as clinically needed.

Interstitial Lung Disease (ILD) / Pneumonitis: Serious and potentially fatal lung conditions have been reported. Monitor for respiratory symptoms and discontinue treatment in severe cases.

Hepatotoxicity: Elevated liver enzymes may occur. Perform liver function tests before and during treatment at regular intervals.

Venous Thromboembolism: Monitor for symptoms of blood clots such as swelling, pain, or breathing difficulty and manage appropriately.

Embryo-Fetal Toxicity: This drug may harm an unborn baby. Patients should be counseled on potential risks.

Pediatric Use: Safety and effectiveness have not been established.

Geriatric Use: No significant difference in safety or effectiveness compared to younger patients.

Renal Impairment: No dose adjustment needed for mild to moderate cases.

Hepatic Impairment: No dose adjustment required for mild to moderate liver impairment.

Protein kinase inhibitor.

Store below 30°C in a dry place. Protect from light and moisture. Keep out of reach of children.