Fulvestrant

Fulvestrant is a prescription medication used to treat certain types of breast cancer in post-menopausal women. Fulvestrant belongs to a group of drugs called estrogen receptor antagonists. It works by blocking the activity of estrogen in breast tissue which stops the cancer from growing.

This medication comes in an injectable form. It is given directly into the muscle of the buttock by a healthcare provider.

Common side effects include injection site pain, nausea, and headache.

Breast cancer is cancer that forms in the cells of the breasts. The development of breast cancer is strongly related to the amount of estrogen the breast is exposed to over time. Some women have hormone receptor positive (ER/PR+) breast cancer. Estrogen receptors are proteins found on the surface of cells. Cancer cells grow in response to estrogen binding to these receptors. Fulvestrant lowers the amount of estrogen in the blood, limiting the amount of estrogen available to bind to these receptors. This slows or stops the growth of cancer cells. 

Hormone receptor testing is done to determine how likely it is that fulvestrant will be an effective treatment. Patients who do not have hormone receptor positive breast cancer are not likely to respond to treatment with fulvestrant.

Fulvestrant is a prescription medication used to treat certain types of breast cancer in post-menopausal women.

Fulvestrant is used to treat women with:

• Hormone receptor (HR)-positive, human epidermal growth factor receptor 2 (HER2)-negative advanced breast cancer, who have gone through menopause and have not been previously treated with endocrine therapy 
• HR-positive advanced breast cancer, who have gone through menopause and whose disease has progressed after endocrine therapy
• HR-positive, HER2-negative advanced breast cancer or breast cancer that has spread to other parts of the body (metastatic), in combination with palbociclib or abemaciclib, in women whose disease has progressed after endocrine therapy

This medication may be prescribed for other uses. Ask your doctor or pharmacist for more information. 

Fulvestrant may be found in some form under the following brand names:

• Faslodex

Common side effects include:

• injection site pain
• nausea
• muscle, joint, and bone pain
• headache
• tiredness
• hot flashes
• vomiting
• loss of appetite
• weakness
• cough
• constipation
• shortness of breath
• increased liver enzymes

Tell your healthcare provider if you have any side effect that bothers you or that does not go away.

Tell your doctor about all the medicines you take including prescription and non-prescription medicines, vitamins, and herbal supplements. Especially tell your doctor if you take warfarin (brand names Coumadin and Jantoven). Your doctor may change the doses of your medicines or monitor for side effects. There are no known drug interactions with fulvestrant.

Symptoms of an allergic reaction to fulvestrant may include:

•  Itching
•  Swelling of your face, lips, tongue or throat
•  Trouble breathing

Blood disorders: Because fulvestrant is administered intramuscularly, it should be used with caution in patients with bleeding diatheses (unusual bleeding tendency or disposition), thromobcytopenia, or anticoagulant use (blood thinners like Coumadin).

Hepatic Impairment: A dose reduction is recommended in patients with moderate hepatic impairment (liver problems). Fulvestrant has not been studied in patients with severe hepatic impairment.

Pregnancy: Women should be advised not to become pregnant while receiving fulvestrant. This medicine may harm the unborn baby.

Medicines can interact with certain foods. In some cases, this may be harmful and your doctor may advise you to avoid certain foods. In the case of fulvestrant there are no specific foods that you must exclude from your diet when receiving this medication.

Before you receive fulvestrant, tell your doctor:

• if you are allergic to fulvestrant or any other medications
• if you have or have ever had any bleeding problems (low level of platelets in your blood or bleed easily)
• if you have liver disease
• about any other medical conditions you have
• if you are pregnant or breastfeeding

Tell your doctor about the medicines you take including prescription and nonprescription medications, vitamins, nutritional supplements, and herbal products. 

Tell your doctor if you are pregnant or plan to become pregnant.

The FDA categorizes medications based on safety for use during pregnancy. Five categories - A, B, C, D, and X, are used to classify the possible risks to an unborn baby when a medication is taken during pregnancy.

Fulvestrant falls into category D. In animal studies, pregnant animals were given this medication and had some babies born with problems. No well-controlled studies have been done in humans, though. Therefore, this medication may be used if the potential benefits to the mother outweigh the potential risks to the unborn child.

It is not known if fulvestrant crosses into human milk. Because many medications can cross into human milk and because of the possibility for serious adverse reactions in nursing infants with use of this medication, a choice should be made whether to stop nursing or stop the use of this medication. Your doctor and you will decide if the benefits outweigh the risk of using fulvestrant.

Your healthcare provider will give you the appropriate amount of fulvestrant by injection into the muscle of your buttock. It is usually administered in a medical facility (doctor's office or hospital).

• Keep all appointments with your doctor.
• If you miss an appointment to receive a dose of fulvestrant, reschedule as soon as possible.

Your doctor will determine the best dose and schedule for you.

Fulvestrant 500 mg should be administered intramuscularly into the buttocks slowly (1 - 2 minutes per injection) as two 5 mL injections, one in each buttock, on days 1, 15, 29 and once monthly thereafter.

A dose of 250 mg is recommended in patients with moderate hepatic impairment to be administered intramuscularly into the buttock slowly (1- 2 minutes) as one 5 mL injection on days 1, 15, 29 and once monthly thereafter.

There is no clinical experience with overdosage in humans. In studies, no adverse reactions were seen in healthy male and female volunteers who received very large intravenous (IV) doses, rather than the usual intramuscular (IM) doses.

Fulvestrant is usually administered by a healthcare provider in a medical setting making it unlikely for an overdose to occur. However, if you believe you or someone you know is experiencing an overdose contact your local poison control center or call 911.