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Generic name: fulvestrant
Brand name: Fasoldex
Dosage form: intramuscular injection
Drug classes: Estrogen receptor antagonists, Hormones / antineoplastics

Medically reviewed by  A Ras MD.

What is fulvestrant used for?

Fulvestrant is a prescription medicine that is used to treat breast cancer. This medicine may be used with other drugs to treat your health condition. If you are also taking other drugs, talk with your doctor about the risks and side effects that may happen.


Fulvestrant Injection for intramuscular administration is an estrogen receptor antagonist. The chemical name is 7-alpha-[9-(4,4,5,5,5-penta fluoropentylsulphinyl) nonyl]estra-1,3,5-(10)-triene-3,17-beta-diol. The molecular formula is C32H47F5O3S and its structural formula is:


Fulvestrant, USP is a white powder with a molecular weight of 606.77. The sterile injection solution is a clear, colorless to yellow viscous liquid supplied in two 5 mL single-dose prefilled syringes each containing 250 mg/5 mL of fulvestrant, USP for intramuscular administration.

Fulvestrant Injection contains the following inactive ingredients in each 5 mL syringe: benzyl alcohol 500 mg (10% w/v) and dehydrated alcohol 500 mg (10% w/v); castor oil 3000 mg (60% w/v), medium chain triglycerides q.s. to 5 mL (10.8% w/v), and nitrogen q.s.

Mechanism of Action

Many breast cancers have estrogen receptors (ER) and the growth of these tumors can be stimulated by estrogen. Fulvestrant is an estrogen receptor antagonist that binds to the estrogen receptor in a competitive manner with affinity comparable to that of estradiol and downregulates the ER protein in human breast cancer cells.

In vitro studies demonstrated that fulvestrant is a reversible inhibitor of the growth of tamoxifen-resistant, as well as estrogen-sensitive human breast cancer (MCF-7) cell lines. In in vivo tumor studies, fulvestrant delayed the establishment of tumors from xenografts of human breast cancer MCF-7 cells in nude mice. Fulvestrant inhibited the growth of established MCF-7 xenografts and of tamoxifen-resistant breast tumor xenografts.

Fulvestrant showed no agonist-type effects in in vivo uterotrophic assays in immature or ovariectomized mice and rats. In in vivo studies in immature rats and ovariectomized monkeys, fulvestrant blocked the uterotrophic action of estradiol. In postmenopausal women, the absence of changes in plasma concentrations of FSH and LH in response to fulvestrant treatment (250 mg monthly) suggests no peripheral steroidal effects.

Before taking fulvestrant, tell your doctor:

  • If you are allergic to fulvestrant; any part of this medicine; or any other drugs, foods, or substances. Tell your doctor about the allergy and what signs you had.
  • If you are breast-feeding. Do not breast-feed while you take fulvestrant and for 12 months after your last dose.

This medicine may interact with other drugs or health problems.

Tell your doctor and pharmacist about all of your drugs (prescription or OTC, natural products, vitamins) and health problems. You must check to make sure that it is safe for you to take fulvestrant with all of your drugs and health problems. Do not start, stop, or change the dose of any drug without checking with your doctor.

What are some things I need to know or do while I take fulvestrant?

  • Tell all of your health care providers that you take fulvestrant. This includes your doctors, nurses, pharmacists, and dentists.
  • Be sure to have regular breast exams and gynecology check-ups. You will also need to do breast self-exams as you have been told.
  • This medicine may affect certain lab tests. Tell all of your health care providers and lab workers that you take fulvestrant.
  • This medicine may affect fertility. Fertility problems may lead to not being able to get pregnant or father a child.
  • This medicine may cause harm to an unborn baby. A pregnancy test will be done before you start fulvestrant to show that you are NOT pregnant.
  • Women must use birth control while taking fulvestrant and for some time after the last dose. Ask your doctor how long to use birth control. If you get pregnant, call your doctor right away.

How is fulvestrant best taken?

Use fulvestrant as ordered by your doctor. Read all information given to you. Follow all instructions closely.

  • It is given as a shot into a muscle.

What do I do if I miss a dose?

  • Call your doctor to find out what to do.

What are the side effects of fulvestrant that I need to call my doctor about immediately?

WARNING/CAUTION: Even though it may be rare, some people may have very bad and sometimes deadly side effects when taking a drug. Tell your doctor or get medical help right away if you have any of the following signs or symptoms that may be related to a very bad side effect:

  • Signs of an allergic reaction, like rash; hives; itching; red, swollen, blistered, or peeling skin with or without fever; wheezing; tightness in the chest or throat; trouble breathing, swallowing, or talking; unusual hoarseness; or swelling of the mouth, face, lips, tongue, or throat.
  • Signs of infection like fever, chills, very bad sore throat, ear or sinus pain, cough, more sputum or change in color of sputum, pain with passing urine, mouth sores, or wound that will not heal.
  • Signs of a urinary tract infection (UTI) like blood in the urine, burning or pain when passing urine, feeling the need to pass urine often or right away, fever, lower stomach pain, or pelvic pain.
  • Low mood (depression).
  • Anxiety.
  • Chest pain or pressure.
  • Shortness of breath.
  • Swelling in the arms or legs.
  • Any unexplained bruising or bleeding.
  • This medicine may cause nerve damage in the area where the injection is given. Call your doctor right away if you have any leg numbness, tingling, or weakness.

What are some other side effects of fulvestrant?

All drugs may cause side effects. However, many people have no side effects or only have minor side effects. Call your doctor or get medical help if any of these side effects or any other side effects bother you or do not go away:

  • Hot flashes.
  • Headache.
  • Feeling dizzy, tired, or weak.
  • Back, bone, joint, or muscle pain.
  • Constipation.
  • Cough.
  • Throat irritation.
  • Stomach pain.
  • Pelvic pain.
  • Trouble sleeping.
  • Sweating a lot.
  • Flu-like signs.
  • Pain in arms or legs.
  • Pain where the shot was given.
  • Diarrhea, throwing up, upset stomach, and feeling less hungry are common with fulvestrant. If these happen, talk with your doctor about ways to lower these side effects. Call your doctor right away if any of these effects bother you, do not get better, or get very bad.

These are not all of the side effects that may occur. If you have questions about side effects, call your doctor. Call your doctor for medical advice about side effects.

You may report side effects to the FDA at 1-800-332-1088. You may also report side effects at https://www.fda.gov/medwatch.

If overdose is suspected:

If you think there has been an overdose, call your poison control center or get medical care right away. Be ready to tell or show what was taken, how much, and when it happened.

How do I store and/or throw out fulvestrant?

  • If you need to store fulvestrant at home, talk with your doctor, nurse, or pharmacist about how to store it.



  • NDC 0591-5019-02          Rx only
  • Fulvestrant Injection
    250 mg/5 mL (50 mg/mL)
  • For Intramuscular Use Only
    This carton contains a total of 500 mg fulvestrant in TWO single-dose prefilled syringes each containing 250 mg/5 mL, and two SafetyGlide™ shielding
    intramuscular injection needles.
  • Discard each syringe after use.
  • Both single-dose prefilled syringes must be administered to receive the 500 mg dose.
  • Contains 2 single-dose prefilled syringes
  • TEVA
  • fulvestrant



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