Fareston (chemical name: toremifene) is a selective estrogen receptor modulator (SERM) used to treat metastatic hormone receptor-positive breast cancer in postmenopausal women.
How Fareston works
Fareston blocks the effects of estrogen on metastatic hormone receptor-positive breast cancer cells by sitting in the estrogen receptors on the cells. If Fareston is in the receptor, estrogen can’t attach to the cancer cell and the cell doesn’t receive estrogen’s signals to grow and multiply.
Fareston will not work on hormone receptor-negative breast cancer.
Is Fareston right for you?
If you’re a postmenopausal woman diagnosed with metastatic hormone receptor-positive breast cancer, Fareston may be a good treatment option for you. It’s important to know that Fareston is not commonly used in the United States.
You should not take Fareston if you have:
a heart rhythm condition called long QT syndrome
low blood potassium levels
low blood magnesium levels
a history of blood clots
endometrial hyperplasia, an overgrowth of the cells in the lining the uterus
You should not take Fareston if you are breastfeeding, pregnant, trying to get pregnant, or if there is any chance that you could be pregnant. Fareston may cause damage to developing embryos. You should use an effective non-hormonal type of birth control while you are taking Fareston. Ask your doctor which type of non-hormonal birth control would be best for you.
What to expect during Fareston treatment
Fareston is a pill taken once per day. Most doctors recommend taking Fareston at the same time each day.
Post-menopausal women diagnosed with metastatic hormone receptor-positive breast cancer take Fareston as long as they are getting benefits from the medicine.
There are certain medicines, supplements, and foods you should avoid if you’re taking Fareston:
You should not take a type of medicine called a CYP3A4 inducer because it decreases the effects of Fareston. This class of medicines includes Rifamate (chemical name: rifampin), an antibiotic used to treat tuberculosis, and Carbatrol (chemical name: carbamazepine), which is used to control certain types of seizures in people with epilepsy. St. John’s wort, an herbal supplement, also is considered a CYP3A4 inducer, so should not be taken with Fareston.
You should not take a type of medicine called a CYP3A4 inhibitor because it increases the effects of Fareston. This class of medicines includes Nizoral (chemical name: ketoconazole) and Sporanox (chemical name: itraconazole), which are used to treat fungal infections; Reyataz (chemical name: atazanavir), used to treat HIV; and nefazodone, used to treat depression.
You should not take a type of medicine called a thiazide diuretic because it can increase the risk of higher-than-normal blood calcium levels. Sometimes called water pills, thiazide diuretics help your body get rid of sodium and water and are a common treatment for high blood pressure. This class of medicines includes Zaroxolyn (chemical name: metolazone), Microzide (chemical name: chlorthalidone), and Lozol (chemical name: indapamide).
You should not take medicines known to prolong the QT interval because Fareston also can prolong the QT interval. The QT interval is a measurement on an electrocardiogram used to evaluate some of your heart’s electrical properties. If the QT interval is too long, it increases the risk of an abnormal heart rhythm. Medicines know to prolong the QT interval include quinidine, used to treat malaria; Pacerone (chemical name: amiodarone), used to treat an irregular heartbeat; Mellaril (chemical name: thioridazine), used to treat schizophrenia; Effexor (chemical name: venlafaxine), used to treat depression and anxiety disorders; erythromycin, an antibiotic; and Zofran (chemical name: ondansetron), used to prevent nausea and vomiting.
You should not drink grapefruit juice or eat grapefruit because they can increase the effects of Fareston.
Fareston side effects
Like almost all breast cancer medicines, Fareston can cause side effects, some of them severe.
The most common side effects of Fareston are:
Fareston also may cause serious side effects, including:
QT prolongation, which can cause a change in your heart’s rhythm. Tell your doctor right away if you have:
shortness of breath
dizziness or fainting
fluttering or palpitations of the heart
lightheadedness that comes and goes
Paying for Fareston
If your doctor prescribes Fareston and you have problems paying for it or getting it covered by insurance, Kyowa Kirin, the company that makes Fareston, has a Patient
Assistance Program and a Copay Assistance Card Program that may be able to help.
Learn more about Paying for Your Care, including information on additional types of financial assistance and cost-lowering tips.
Fareston (toremifene) prescribing information. Kyowa Kirin, Inc. USA. Available at: https://fareston.aspnprograms.com/siteforms/fareston-pi.pdf
— Last updated on January 13, 2022, 4:09 PM