I. Drug Name

Generic Name: Abemaciclib Tablets

English Name: Abemaciclib

Brand Names: Verzenio, BESIDX

Dosage Form: Oral Film-Coated Tablets

Specification: 150 mg per tablet; 56 tablets per box

Manufacturer: Laos Da Xiong Pharmaceutical Co., Ltd.

Regulatory Approval No.: 04 L1097/24

II. Pharmacological Actions

Pharmacological Classification: Cyclin-Dependent Kinase 4/6 (CDK4/6) Inhibitor

Mechanism of Action:

In estrogen receptor-positive (ER+) breast cancer cells, Cyclin D1 binds to CDK4/6, driving the cells from the G1 phase into the S phase and promoting cell division and proliferation.

Abemaciclib selectively inhibits the activity of CDK4/6, thereby blocking the phosphorylation of the Retinoblastoma protein (Rb). This leads to cell cycle arrest in the G1 phase and inhibits the proliferation of tumor cells.

Compared to other drugs in the same class, Abemaciclib demonstrates higher selectivity for CDK4 than for CDK6; this may be one of the reasons for its higher single-agent activity and higher incidence of diarrhea.

III. Indications

Abemaciclib is indicated for the treatment of adult patients with hormone receptor-positive (HR+) and human epidermal growth factor receptor 2-negative (HER2-) advanced or metastatic breast cancer:

1. In Combination with Endocrine Therapy:

In combination with an aromatase inhibitor (e.g., anastrozole) as initial endocrine-based therapy for postmenopausal women.

In combination with fulvestrant for patients whose disease has progressed following prior endocrine therapy.

2. As Monotherapy:

For patients whose disease has progressed following prior endocrine therapy and chemotherapy in the metastatic setting.

IV. Dosage and Administration

Recommended Dosage (varies depending on the treatment regimen):

Combination Therapy: 150 mg, taken orally twice daily (approximately every 12 hours).

Monotherapy: 200 mg, taken orally twice daily (approximately every 12 hours). Administration:

Swallow tablets whole; may be taken with or without food.

If a dose is missed, do not take the missed dose unless more than 6 hours remain before the next scheduled dose. Instead, take the next scheduled dose as soon as possible, and then resume the normal dosing schedule. Do not take a double dose to make up for a missed dose.

If vomiting occurs after taking the medication, do not take a replacement dose; wait until the next scheduled time to take the regular dose.

V. Contraindications

Patients with a history of severe hypersensitivity to abemaciclib or to any of the excipients.

VI. Warnings and Precautions

1. Diarrhea: Diarrhea is the most common and prominent adverse reaction associated with abemaciclib; it may be severe and lead to dehydration or infection.

At the onset of treatment, patients should be provided with anti-diarrheal agents (e.g., loperamide) to have on hand and should be instructed to use them immediately upon the first occurrence of loose stools.

Patients must be advised to increase their fluid and electrolyte intake. Depending on the severity of the diarrhea, it may be necessary to temporarily withhold the medication, reduce the dosage, or permanently discontinue treatment.

2. Neutropenia:

May cause severe neutropenia, including febrile neutropenia.

Monitor complete blood counts prior to initiating treatment, every two weeks for the first two months of treatment, monthly thereafter, and as clinically indicated.

Depending on the severity of the neutropenia, it may be necessary to temporarily withhold the medication, reduce the dosage, or provide supportive care.

3. Interstitial Lung Disease (ILD)/Pneumonitis:

Severe, and potentially fatal, ILD/pneumonitis may occur.

In patients presenting with symptoms suggestive of ILD/pneumonitis (e.g., dyspnea, cough, hypoxia, or infiltrates on chest imaging), immediately interrupt treatment and evaluate the patient. If ILD/pneumonitis is confirmed, permanently discontinue abemaciclib.

4. Hepatotoxicity:

May cause elevations in ALT (alanine aminotransferase) and AST (aspartate aminotransferase).

Monitor liver function tests prior to initiating treatment, every two weeks for the first two months of treatment, monthly thereafter, and as clinically indicated.

Depending on the severity of the hepatotoxicity, it may be necessary to temporarily withhold the medication, reduce the dosage, or permanently discontinue treatment. 5. Venous Thromboembolism (VTE):

Deep vein thrombosis (DVT) and pulmonary embolism (PE) may occur.

Patients should be monitored for signs and symptoms of VTE and treated as clinically indicated.

6. Embryo-Fetal Toxicity:

Based on its mechanism of action, abemaciclib may cause fetal harm when administered to pregnant women.

Women of reproductive potential should use effective contraception during treatment and for at least 3 weeks following the last dose.

Male patients should be advised of the potential risk to the fetus.

VII. Adverse Reactions

Very Common (>10%) Serious and/or Major Adverse Reactions:

Gastrointestinal: Diarrhea (very common and potentially severe), nausea, vomiting, abdominal pain, decreased appetite, stomatitis.

Hematologic and Lymphatic Systems: Neutropenia, leukopenia, anemia, thrombocytopenia.

Systemic: Fatigue/asthenia, infection.

Hepatobiliary System: Elevated ALT/AST.

Skin and Subcutaneous Tissues: Rash, alopecia, pruritus.

Nervous System: Headache, dysgeusia.

Laboratory Abnormalities:

Elevated creatinine, elevated serum creatine phosphokinase (CPK).

VIII. Drug Interactions

Strong CYP3A Inhibitors (e.g., clarithromycin, itraconazole, ritonavir):

Co-administration significantly increases abemaciclib plasma concentrations, thereby increasing the risk of adverse reactions.

Avoid co-administration. If co-administration is unavoidable, reduce the abemaciclib dose by 50 mg (e.g., from 150 mg to 100 mg, twice daily).

Strong CYP3A Inducers (e.g., rifampin, carbamazepine, St. John’s wort):

Co-administration significantly decreases abemaciclib plasma concentrations, potentially compromising efficacy.

Avoid co-administration. If co-administration is unavoidable, consider gradually increasing the abemaciclib dose, up to a maximum of 200 mg twice daily.

IX. Use in Specific Populations

Pregnancy: May cause fetal harm. Advise pregnant women of the potential risk to the fetus. Lactation: It is recommended to discontinue breastfeeding during treatment and for at least 3 weeks following the last dose.

Pediatric Use: Safety and efficacy in children have not been established.

Geriatric Use: In patients aged 65 years and older, no significant differences in overall safety were observed compared to younger patients.

Hepatic/Renal Impairment:

Hepatic Impairment:

No dose adjustment is required for patients with mild (Child-Pugh A) hepatic impairment.

For patients with moderate (Child-Pugh B) or severe (Child-Pugh C) hepatic impairment, a dose reduction of approximately 50 mg is recommended (e.g., from 150 mg to 100 mg, twice daily).

Renal Impairment:

No dose adjustment is required for patients with mild to moderate renal impairment (creatinine clearance 30–89 mL/min).

For patients with severe renal impairment (creatinine clearance <30 mL/min) or those requiring dialysis, data are limited; use with caution.

X. Overdosage

Symptoms: Symptoms are expected to be an exacerbation of adverse reactions, such as severe diarrhea, myelosuppression, hepatotoxicity, etc.

Management: Discontinue the drug immediately, institute supportive care, and provide symptomatic treatment, including close monitoring of blood counts and vital signs.

XI. Clinical Pharmacology

Pharmacokinetics: Abemaciclib is well absorbed following oral administration, reaching peak concentrations in approximately 8 hours. Food does not affect its absorption. *In vivo*, it is primarily metabolized via CYP3A4. Fecal excretion is its primary route of elimination.

XII. Patient Counseling Information

1. Diarrhea Management: Understand how to prevent and manage diarrhea; keep anti-diarrheal medications on hand; and promptly report severe or persistent diarrhea to your doctor.

2. Regular Monitoring: Understand the importance of regular blood tests to monitor blood counts and liver function.

3. Signs of Infection: Immediately report fever, chills, or other signs of infection.

4. Pulmonary Symptoms: Immediately report new or worsening shortness of breath, cough, or similar symptoms.

5. Signs of Thrombosis: Recognize and report leg swelling/pain, sudden chest pain, or difficulty breathing.

6. Contraception Requirements: Patients of reproductive potential must understand and comply with contraception requirements. Finally, I would like to emphasize once again: please be sure to follow the specific instructions provided by your attending physician and pharmacist. Should you experience any questions or discomfort during the course of your treatment, please communicate immediately with your medical team.