Fulvestrant belongs to the group of cancer-fighting medications called antineoplastics, and specifically to the type of antineoplastics known as antiestrogens. It treats certain types of breast cancer by blocking the effects of the hormone estrogen in the body. This prevents the growth of the types of breast cancer cells that require estrogen for growth and survival.

This medication may be available under multiple brand names and/or in several different forms. Any specific brand name of this medication may not be available in all of the forms or approved for all of the conditions discussed here. As well, some forms of this medication may not be used for all of the conditions discussed here.

Your doctor may have suggested this medication for conditions other than those listed in these drug information articles. If you have not discussed this with your doctor or are not sure why you are taking this medication, speak to your doctor. Do not stop taking this medication without consulting your doctor.

Do not give this medication to anyone else, even if they have the same symptoms as you do. It can be harmful for people to take this medication if their doctor has not prescribed it.

Fulvestrant is available only as an injection into the muscle of the buttocks. When starting treatment, 500 mg is given as 2 injections of 250 mg, once every 2 weeks for 3 doses. After this, a dose is given every 28 days. Some people can be taught to give this medication to themselves. If this is the case, make sure you understand exactly how it is to be injected as instructed by your doctor or nurse. The medication should be a clear, colourless-to-yellow, thick liquid. Do not use the medication if it appears cloudy or discoloured, or if there are particles floating in it.

Many things can affect the dose of medication that a person needs, such as body weight, other medical conditions, and other medications. If your doctor has recommended a dose different from the ones listed here, do not change the way that you are taking the medication without consulting your doctor.

It is important to use this medication exactly as prescribed by your doctor.

If you miss a dose, take it as soon as possible and continue with your regular schedule. If it is almost time for your next dose, skip the missed dose and continue with your regular dosing schedule. Do not take a double dose to make up for a missed one. If you are not sure what to do after missing a dose, contact your doctor or pharmacist for advice.

Store this medication in its original package in the refrigerator, protect it from light, and keep it out of the reach of children.

Each mL of clear, colourless-to-yellow, viscous liquid for injection contains 50 mg of fulvestrant. Nonmedicinal ingredients: ethanol 96%, benzyl alcohol, benzyl benzoate, and castor oil.

Do not use this medication if you:

• are allergic to fulvestrant or any ingredients of the medication
• are breast-feeding
• are pregnant

Many medications can cause side effects. A side effect is an unwanted response to a medication when it is taken in normal doses. Side effects can be mild or severe, temporary or permanent. The side effects listed below are not experienced by everyone who takes this medication. If you are concerned about side effects, discuss the risks and benefits of this medication with your doctor.

The following side effects have been reported by at least 1% of people taking this medication. Many of these side effects can be managed, and some may go away on their own over time.

Contact your doctor if you experience these side effects and they are severe or bothersome. Your pharmacist may be able to advise you on managing side effects.

• diarrhea
• headache
• hot flashes
• loss of appetite
• mild pain, redness, or swelling around the site of the injection
• nausea
• rash
• vomiting
• weakness

Although most of the side effects listed below don't happen very often, they could lead to serious problems if you do not seek medical attention.

Check with your doctor as soon as possible if any of the following side effects occur:

• signs of a bladder infection (frequent urination, pain or burning feeling when urinating, smelly urine)
• signs of liver problems (e.g., nausea, vomiting, diarrhea, loss of appetite, weight loss, yellowing of the skin or whites of the eyes, dark urine, pale stools)

Stop taking the medication and seek immediate medical attention if any of the following occur:

• signs of an allergic reaction (hives; difficulty breathing; swelling of the face, tongue, or throat)

Some people may experience side effects other than those listed. Check with your doctor if you notice any symptom that worries you while you are taking this medication.

Before you begin using a medication, be sure to inform your doctor of any medical conditions or allergies you may have, any medications you are taking, whether you are pregnant or breast-feeding, and any other significant facts about your health. These factors may affect how you should use this medication.

Driving: This medication usually does not make you drowsy or impair your ability to drive or operate machinery. However, it may make some people feel weak. Do not drive or operate machinery if you feel weak.

Kidney function: People with kidney problems or poor kidney function should be closely monitored by their doctor while taking this medication.

Lab test results: Fulvestrant can cause falsely high amounts of estradiol (a type of estrogen) in blood tests. This can lead to misinterpretation of whether you are premenopausal or postmenopausal. Make sure all the medical professionals involved in your care know you are taking this medication.

Liver disease: Fulvestrant may reduce liver function and can cause liver failure. Liver disease or reduced liver function may cause this medication to build up in the body, causing side effects. If you have liver problems, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

If you experience symptoms of liver problems such as fatigue, feeling unwell, loss of appetite, nausea, yellowing of the skin or whites of the eyes, dark urine, pale stools, abdominal pain or swelling, and itchy skin, contact your doctor immediately.

Risk of bleeding: Because this medication is given by intramuscular (IM) injection, people with an increased risk of bleeding, such as those taking blood thinners (e.g., warfarin) or those with medical conditions that can cause bleeding, should take extra care when giving themselves an injection.

Pregnancy: This medication should not be used during pregnancy. It may cause severe harm to the developing baby if it is used by the mother during children. If you become pregnant while taking this medication, contact your doctor immediately.

Breast-feeding: It is not known if fulvestrant passes into breast milk. If you are a breast-feeding mother and are taking this medication, it may affect your baby. Talk to your doctor about whether you should continue breast-feeding.

Children: The safety and effectiveness of using this medication have not been established for children.

Tell your doctor or prescriber about all prescription, over-the-counter (non-prescription), and herbal medications that you are taking. Also tell them about any supplements you take. Since caffeine, alcohol, the nicotine from cigarettes, or street drugs can affect the action of many medications, you should let your prescriber know if you use them. Depending on your specific circumstances, your doctor may want you to:

• stop taking one of the medications,
• change one of the medications to another,
• change how you are taking one or both of the medications, or
• leave everything as is.

An interaction between two medications does not always mean that you must stop taking one of them. Speak to your doctor about how any drug interactions are being managed or should be managed.