Faslodex Fulvestrant Injection

1. Indications and Usage
Breast Cancer:
Indicated for the treatment of hormone receptor (HR)-positive, human epidermal growth factor receptor 2 (HER2) -negative locally advanced or metastatic breast cancer in postmenopausal women.
Monotherapy: In patients with disease progression following anti-estrogen therapy.
Combination Therapy: In combination with palbociclib, ribociclib, or abemaciclib as initial endocrine-based therapy.
2. Dosage and Administration
Route of Administration:
For Intramuscular (IM) Injection ONLY.
Recommended Dosage:
Standard Regimen: 500 mg administered on Days 1, 15, and 29 (monthly thereafter) as a single intramuscular injection.
Note: Prior to May 2016, a 250 mg dose was standard; the 500 mg dose is now the recommended therapeutic dose.
Administration Instructions:
Administer as a slow intramuscular injection into the buttock.
The total dose (500 mg) is administered as two consecutive 250 mg/5 mL injections (one in each buttock).
Missed Dose: If a dose is missed, administer as soon as possible and resume the monthly schedule.
3. Mechanism of Action
Estrogen Receptor Antagonist:
Fulvestrant is a steroidal antiestrogen that binds to the estrogen receptor (ER) with similar affinity to estradiol.
Receptor Downregulation:
Unlike selective estrogen receptor modulators (SERMs) such as tamoxifen, fulvestrant has no agonist activity. It blocks the ER, inhibits its dimerization, and induces a conformational change that leads to the proteasomal degradation of the receptor. This results in a significant reduction of ER levels and inhibition of tumor cell growth.
4. Safety and Warnings
Hepatotoxicity:
Elevations in liver enzymes (ALT, AST) have been reported. Monitor liver function tests (LFTs) prior to initiation and as clinically indicated during treatment.
Thromboembolism:
Venous thromboembolism (e.g., DVT, PE) can occur, particularly in patients with advanced breast cancer. Monitor for signs of thrombosis.
Embryo-Fetal Toxicity:
Can cause fetal harm. Pregnancy testing is recommended before initiating treatment. Females of reproductive potential must use effective contraception during treatment.
5. Adverse Reactions
Most Common:
Nausea, fatigue, vomiting, headache, injection site reaction, hot flashes, diarrhea, decreased appetite, and abnormal liver function tests.
6. Drug Interactions
CYP3A4 Substrates:
Fulvestrant is primarily metabolized by CYP3A4.
Strong CYP3A4 Inhibitors/Inducers:
Clinical studies indicate that co-administration with strong CYP3A4 inhibitors (e.g., ketoconazole) or inducers (e.g., rifampin) does not significantly alter fulvestrant exposure; therefore, dose adjustment is generally not required.
7. Pharmaceutical Information
Chemical Composition:
Active Ingredient: Fulvestrant.
Appearance: Clear, colorless to light brownish-yellow, viscous liquid.
Storage: Store in the original carton at 2°C to 8°C (36°F to 46°F). Do not freeze or shake.