Fulvestrant - Uses, Mechanism of Action, Dosage, Warnings, and Side Effects

Drug Overview:

Fulvestrant is a potent estrogen inhibitor drug used in the treatment of breast cancer in advanced stages. The Food and Drug Administration (FDA) has approved Fulvestrant as a single-agent therapy (monotherapy) in the treatment of breast cancer for post-menopausal women. Fulvestrant is an estrogen receptor antagonist or inhibitor available in injectable doses of 250 mg (milligrams) and 500 mg. Fulvestrant 500 mg is administered intramuscularly (IM) on days 1, 15, and 29 and then once per month in the gluteal (buttocks) region. Fulvestrant is used either as a single agent therapy or in combination therapy with other drugs like Palbociclib or Ribociclib for managing hormone blockers for breast cancer in postmenopausal women.

How Fulvestrant Works?

Fulvestrant works by binding to the receptors of breast cancer and inhibiting the growth of the tumor by cessation and degradation of the receptors responsible for the tumor growth. This hormone suppression mechanism is aimed at addressing the biological processes that commonly lead to tumor formation in HR-positive breast cancers.

What Is Fulvestrant Used For?

• Fulvestrant is used as monotherapy or single-agent therapy treatment for breast cancer in postmenopausal women.

• It can also be used in combination therapy with drugs like Ribociclib and Palbociclib for the management of breast cancer in advanced stages where there is metastasis.

Doses:

• For Single Agent Therapy: Fulvestrant hormone shots (injections) of 500 mg are to be given intramuscularly (IM) as two 5 ml injections on days 1, 15, 29, and once per month in the gluteal region. Fulvestrant injection of 250 mg is also used intramuscularly, such as one 5 ml injection on days 1, 15, 29, and once per month in patients who are systemically compromised. Single-agent therapy or monotherapy is recommended in patients with hormone-receptor (HR) positive and HER2 (hormone estrogen receptor) negative with no history of endocrine therapy.

• For Combination Therapy: Fulvestrant hormone shot (injection) of 500 mg is injected intramuscularly, similar to the single agent therapy technique. It is given in combination with other drugs like Palbociclib, which is given orally at the dose of 125 mg once daily for twenty-one days.

• Fulvestrant injection of 500 mg is also given in combination with Ribociclib, which is given at the dose of 600 mg orally for 21 days.

• The combination therapy is usually recommended by doctors in patients who are HR-positive (metastatic cancer), HER2 (hormone estrogen receptor), a negative cancer that has progressed to the advanced stage due to a history of endocrine therapy.

Warning:

• Risk of Bleeding: As the drug is administered through an intramuscular (IM) route there is a risk of bleeding. Cautions should be taken while administering this drug to patients with bleeding disorders and patients who are on anticoagulants or blood thinners medications.

• Hepatic Impairment: Liver impairment has been reported in a few patients. The drug Fulvestrant in a dose of 250 mg is prescribed in such patients.

• Fetal Toxicity: Few clinical studies have reported harm to the fetus when the drug is administered in pregnant females.

For Patients:

What Do You Need to Know About Postmenopausal Breast Cancer?

After menopause at 55 years of age, the risk of breast cancer increases in females because of the sudden shoot in the levels of estrogen in the body. Estrogen is responsible for the growth of the uterus and breast tissue. Women who undergo hormonal therapy (HT) after menopause are more at risk of developing breast cancer. People who are obese are most likely at risk of getting breast cancer. So, it is advised to discuss the side effects of hormonal therapy with your doctor before starting the therapy.

How Can We Reduce the Risk of Breast Cancer After Menopause?

A few minor changes in your daily lifestyle can reduce the risk of breast cancer.

Some changes that need to be inculcated are:

• Exercise daily.

• Have a balanced diet.

• Avoid smoking and consuming alcohol.

• Avoid gaining unnecessary weight by keeping a check on your body mass index (BMI).

• Reduce the number of doses of hormonal therapy.

• In the case of females with a family history of breast cancer, it is recommended to undergo breast screening programs and mammography to detect any precancerous breast conditions.

• Preventive breast cancer medications like hormone blockers for breast cancer (estrogen blockers) can be taken under the prescription of a doctor in the case of females who are suspected of having an increased risk of breast cancer.

• Preventive surgical management, like prophylactic mastectomy (removal of all breast tissue), is recommended by doctors for women who are at heightened risk of getting breast cancer based on the symptoms.

Is Hormonal Therapy Safe?

The hormonal therapy used after menopause increases the risk of cancer tremendously.

It is recommended to discuss the advantages and disadvantages of hormonal therapy (estrogen and progesterone) with your doctor before initiating the therapy.

What Are the Causes of Breast Cancer?

One of the following risk factors can increase the chances of breast cancer:

• Hormonal changes (sudden hike in the levels of estrogen and progesterone hormones after menopause).

• Unhealthy lifestyle.

• Chronic smoking.

• Excessive alcohol and caffeine intake.

• Hereditary- family history of breast cancer.

• Obesity.

• Radiation exposure.

• Menopause starts at an older age.

• Women having their first child after the age of 30 have an increased risk of breast cancer.

• Women with no history of pregnancy are at higher risk of breast cancer than women with multiple pregnancies.

• Hormonal therapy - women who undergo hormonal therapy (HT) after menopause are at increased risk.

Learn More About Fulvestrant:

What Is Fulvestrant?

Fulvestrant is a hormone therapy prescribed for certain types of breast cancer. It is an estrogen receptor antagonist that binds to estrogen receptors in breast cancer cells, slowing their growth. FDA approval was granted in 2002 after Phase 3 trials showed patients on Fulvestrant took longer to worsen their cancer compared to those on Anastrozole. Fulvestrant is only approved for specific types of breast cancer in women, and doctors prescribe it only if proven effective. It is given as an injection into the buttock muscle once a month, with the dose adjusted based on effectiveness and side effects. Fulvestrant may also be combined with other medications for breast cancer treatment.

When and Why to Take Fulvestrant Medication?

• For women who are diagnosed with post-menopausal breast cancer, based on symptoms like frequent headaches, hot flush, mood swings, breast screening, and mammography, the doctor will prescribe you the medication Fulvestrant. Fulvestrant medications help decrease excessive estrogen levels in the body, thereby reducing post-menopausal symptoms.

• Based on various clinical trials, Fulvestrant has proven its efficacy in the treatment of breast cancer in women who were in advanced stages with cancer spreading to different body parts (showing distant metastasis). The effectiveness of the drug was proven to have satisfactory results either taken as monotherapy or as a combination therapy with other drugs like Palbociclib.

Why Is Fulvestrant Prescribed?

Based on the clinical trials in women who were EHR (estrogen hormone receptor) positive and in advanced stages of breast cancer, the drug Fulvestrant has shown a reduction in estrogen hormone levels and a decrease in the symptoms associated with post-menopausal breast cancer. Patients with localized breasts have also shown a decreased progression in breast cancer within 21 months of medications. It has also shown some improvement in patients with metastatic breast cancers.

What Fulvestrant Precautions Should I Follow?

• Inform your doctor if you have any history of allergies to any medications.

• Inform your doctor in case you have any systemic medical conditions like diabetes, liver diseases, or bleeding disorders like hemophilia and bleeding diathesis.

• Inform your doctor if you are under any medications like blood thinners or anticoagulants like Warfarin.

• Any habits like alcohol and smoking should be informed to the doctor.

• Women who are planning pregnancy, breastfeeding mothers, or pregnant women should inform the doctor about their respective health status.

Starting Fulvestrant Medications:

How Should I Use Fulvestrant?

Fulvestrant should be taken as prescribed by the doctor in accurate doses and frequency.

Fulvestrant is available in injection form in the dose of 250 mg per 5ml vial, and two vials are used for the 500 mg dose. It is given intramuscularly by the doctor or nurse slowly into the gluteal region (buttocks). It is prescribed once every two weeks. The first three doses are given on days 1, 15, and 29, followed by once a month further.

Things to Do After You Start Taking Fulvestrant

• Inform your doctor in case you have any Fulvestrant side effects like swelling on the Fulvestrant injection site, swelling in the feet or ankles, shortness of breath, and chest pain.

• Check for the improvement in the symptoms and keep track of them.

• Inform the doctor about improvement in the symptoms noticed during the follow-up sessions.

What Are the Side Effects of Fulvestrant?

The common Fulvestrant side effects involve:

• Pain and redness on the injection site.

• Nausea and vomiting.

• Diarrhea.

• Stomach pain.

• Sore throat.

• Weakness.

• Swelling in feet and ankles.

• Anxiety.

• Ambiguous vaginal bleeding.

• Insomnia (sleepless nights).

• Bone and joint pain.

Some serious Fulvestrant side effects are:

• Shortness of breath.

• Pain in the chest.

• Burning sensation on urination.

• Pale eyes and skin.

• Swelling of the lips, tongue, face, and throat.

• Numbness in the legs.

• Rashes.

Also, various other side effects are associated with Fulvestrant medication. In case any side effects are noticed, it is advised to report it to the doctor immediately.

Dietary Alterations:

There is no specific diet alteration needed when you are on Fulvestrant unless any changes are advised by the doctor. Patients can continue to have a regular healthy, and balanced diet.

What Should Be Done if You Forgot a Dose?

If you missed visiting the doctor for the scheduled appointment for the dose, inform your doctor about it as early as possible.

What Should Be Done in Case of Fulvestrant Overdose?

In case of any overdose, reach out to the poison control helpline. It is advised to call the emergency number immediately in case a patient has collapsed or is having breathlessness.

How to Store Fulvestrant?

Fulvestrant should ideally be stored at a temperature of two to eight degrees Celsius. It should be stored in its original container until used. It should be kept away from sunlight.

Avoid Self-Prescription:

The medicine should be used strictly under the doctor's prescription and supervision. After recording a thorough history, presenting symptoms, and running confirmatory diagnostic scans for the condition, the doctor will prescribe the accurate drug with the required doses and drug schedule based on the diagnosis and examination.

Staying On Fulvestrant

• Take the Fulvestrant in the doses and frequency specified by the doctor. Do not miss any Fulvestrant injection schedule provided by the doctor.

• If any dose is missed, inform the doctor as soon as possible.

• Fulvestrant has proven to decrease the progression of cancer within 21 months of medications, even in the advanced stages.

• In case of any side effects noticed, inform the doctor immediately.

• Keep track of the improvement of symptoms noticed after starting the medications and share with your doctor during the follow-up visits.

• Always inform your doctor if any progression or worsening of symptoms is observed.

For Doctors:

Indications:

The drug Fulvestrant is indicated in patients with post-menopausal breast cancer.

Pharmacology:

Mechanism of Action:

Women with post-menopausal breast cancer are estrogen receptor (ER) positive due to a sudden shoot of the estrogen levels in the body. The drug Fulvestrant acts by binding to these estrogen receptors and thereby blocking or degrading the receptors, which are seeding the tumor growth.

Pharmacodynamics:

Fulvestrant medication has shown a reduction in the estrogen receptors with increasing doses in the patient after the medications are started. It has also shown a decrease in estrogen-regulating protein expression after the administration of Fulvestrant with increasing doses.

Chemical Taxonomy:

Ingredients:

Active Ingredient: The only active ingredient is Fulvestrant.

Inactive Ingredients:

• Alcohol.

• Benzyl alcohol.

• Castor oil.

• Benzyl benzoate.

Absorption:

• Fulvestrant is observed slowly.

• The maximum plasma concentration peaks after seven days.

Distribution:

• Fulvestrant steady-state volume is around three to five L/kg (liter per kilogram).

• Fulvestrant has 99 percent binding efficiency to plasma proteins or lipoprotein particles.

Metabolism:

• Fulvestrant metabolizes by oxidation, hydroxylation, and conjugation with glucuronic acid to form less active metabolites.

Elimination:

• The total plasma clearance rate is 226 mL/min.

• The half-life of the Fulvestrant is around 40 days.

Toxicity:

• No mutagenic or overdose clinical experience has been reported yet based on the clinical trials of Fulvestrant.

Warning and Precautions:

• With adequate caution, Fulvestrant can be administered in patients with bleeding disorders or on anticoagulant therapy.

• In a few patients, hepatic (liver) impairment was observed, so drugs are prescribed at a minimal dose of 250 mg for these patients.

• Fulvestrant is toxic to the fetus, so it is advised not to become pregnant while on medication.

Doses and Forms:

• Fulvestrant is administered intramuscularly.

• Fulvestrant is available in clear, colorless, viscous liquid form.

• Fulvestrant is available in doses of 250 mg per 5 mL vial.

Administration of the Drug:

Fulvestrant is administered intramuscularly once every two weeks on days 1, 15, and 29 followed by once a month further.

Who Should Not Use Fulvestrant?

Fulvestrant is contraindicated in patients with allergic reactions to the drugs (hypersensitivity).

Drug Interactions:

There is no known drug interaction of Fulvestrant reported yet.

Other Specifications:

Fulvestrant in Pregnant and Lactating Women:

• Fulvestrant has harmful effects on the fetus, so it is advised not to become pregnant while on medications and inform the doctor prior about the condition.

• The side effects of the drug on the fetus in the lactating mother are yet not known. As many drugs are excreted from the milk, so the use of Fulvestrant in a lactating mother is yet to be known.

Fulvestrant in Pediatric Patients:

There were few adverse effects like abnormal vaginal bleeding, redness and swelling at the injection site, increased heart rate, and hot flush reported in the clinical trials conducted in pediatric patients.

Fulvestrant in a Patient With Renal Impairment:

The renal clearance of Fulvestrant is very low. The studies for the use of the Fulvestrant in renal impairment have not yet been conducted.

Fulvestrant in a Patient With Hepatic Impairment:

Fulvestrant is mostly metabolized by the liver. So safety and precautionary doses of 250 mg are indicated in patients with mild liver impairment.