From the Guidelines
Fulvestrant is administered as an intramuscular injection, typically given as two separate 5 mL injections (one in each buttock) for a total dose of 500 mg, with a standard dosing schedule that begins with the initial 500 mg dose, followed by 500 mg doses at 2 weeks, 4 weeks, and then monthly thereafter, as supported by the most recent and highest quality study 1. The administration of fulvestrant via intramuscular injection allows for sustained release of the medication, maintaining therapeutic levels in the body between monthly injections.
- The injections must be given slowly into the buttock muscle by a healthcare professional, as the medication is formulated as a solution in oil and cannot be given intravenously.
- Patients should be positioned lying down or standing for the injection.
- The injection sites should be rotated to prevent tissue damage or discomfort. Fulvestrant works as an estrogen receptor antagonist by binding to estrogen receptors and triggering their degradation, thereby blocking estrogen's ability to stimulate breast cancer cell growth. Common injection site reactions may include pain, redness, or swelling, as noted in the studies 1. The use of a loading dose followed by a high dose of fulvestrant is the preferred dose and schedule for fulvestrant administration, as it has been shown to be effective in improving patient outcomes, including progression-free survival and overall survival, as demonstrated in the study 1.
From the FDA Drug Label
PACKAGE LABEL. PRINCIPAL DISPLAY PANEL NDC 70771-1626-2 Fulvestrant Injection 250 mg/5 mL (50 mg/mL) For Intramuscular Use Only Both single-dose prefilled syringes must be administered to receive the 500 mg dose This carton contains a total of 500 mg fulvestrant in TWO single-dose prefilled syringes each containing 250 mg/5 mL, and two Safety Glide™ shielding intramuscular injection needles. Both single-dose prefilled syringes must be administered to receive the 500 mg dose.
Fulvestrant is given intramuscularly. The recommended dose is administered using two single-dose prefilled syringes, each containing 250 mg/5 mL, to receive a total dose of 500 mg 2.
From the Research
Administration of Fulvestrant
- Fulvestrant is a parenteral agent, indicating it is given via injection 3.
- The typical dosing regimen for fulvestrant is 500 mg, which has been shown to be more effective than 250 mg without significant differences in toxicity 4, 5.
- Fulvestrant is usually administered every 28 days, with an additional loading dose given on day 14 for the 500 mg regimen 5.
- As a selective estrogen receptor down-regulator (SERD), fulvestrant binds, blocks, and degrades the estrogen receptor, leading to complete inhibition of estrogen signaling through the receptor 5, 6.
Clinical Use
- Fulvestrant is licensed for use in postmenopausal women with hormone receptor-positive advanced breast cancer that has progressed on prior endocrine therapy 3.
- It is also used as a first-line endocrine treatment in patients with metastatic breast cancer, with real-world data showing effectiveness in this setting 7.
- Fulvestrant has been used in combination with other therapies, such as CDK4/6 inhibitors and drugs targeting the PI3K/AKT/mTOR pathway, to improve treatment outcomes 5.