Cancer Home > Precautions and Warnings With Toremifene
Although toremifene can be an effective breast cancer treatment, it may increase the risk for heart problems, drug interactions, or other potentially serious complications. This medicine may not be safe for people who have a history of heart rhythm problems, heart attacks, or strokes. Precautions and warnings with toremifene also apply to women who are pregnant or breastfeeding.
You should talk with your healthcare provider prior to taking toremifene citrate (Fareston®) if you have:
- Heart rhythm problems, including a condition known as QT prolongation or long QT syndrome
- Been told you have an electrolyte imbalance, such as low blood potassium (hypokalemia) or magnesium (hypomagnesemia)
- Congestive heart failure
- Unexplained vaginal bleeding
- A history of a blood clot or stroke
- Had endometrial hyperplasia (unusual growth and thickening of the lining of the uterus)
- Cancer that has spread to your bone
- Liver disease, such as hepatitis, cirrhosis, or liver failure
- Low white blood cells or platelets
- Any allergies, including to foods, dyes, or preservatives.
Also, let your healthcare provider know if you are:
- Pregnant or thinking of becoming pregnant
Make sure to tell your healthcare provider about all other medications you are taking, including prescription and nonprescription medicines, vitamins, and herbal supplements.
Some warnings and precautions to be aware of prior to taking this drug include the following:
- Toremifene may cause a potentially dangerous heart problem known as QT prolongation, which can lead to a life-threatening arrhythmia (abnormal heartbeat). Because low blood potassium or magnesium levels increase your risk for QT prolongation, your healthcare provider will check your levels with a simple blood test before you start treatment and periodically thereafter.
If you are at risk for QT prolongation, your healthcare provider may want to check the electrical activity of your heart with an electrocardiogram (ECG) before you start toremifene.
- Some women, particularly those whose cancer has spread to the bone, may experience a sudden increase in symptoms, such as an increase in the size of their tumors, muscle and bone pain, and skin rash, shortly after starting toremifene. Blood calcium levels may also increase. This reaction (known as tumor flare) is usually only temporary, and does not mean the medicine is not working. If your blood calcium levels are extremely high, however, your healthcare provider may recommend you stop taking this drug.
- Toremifene may cause the lining of the uterus (the endometrium) to grow and thicken, which could increase your chance of getting endometrial cancer. Some women who were treated with this medication developed endometrial cancer. You should report any unexplained vaginal bleeding to your healthcare provider, as it may be a sign of this disease.
- Because of the risks associated with its use, this medication may not be the best choice for women who have had a blood clot. It also generally should not be used for a long period of time in women who have had endometrial hyperplasia (abnormal growth and thickening of the endometrium).
- Your healthcare provider will order certain blood tests periodically during treatment to make sure you are not developing potentially dangerous toremifene side effects. This may include blood tests to check your calcium levels, liver function, platelets, and white blood cells. Make sure to keep all your healthcare and laboratory appointments during treatment.
- Toremifene may react with a number of other medications (see Drug Interactions With Toremifene).
- Toremifene is a pregnancy Category D medication, which means it may harm an unborn child if taken during pregnancy (see Fareston and Pregnancy).
- It is unknown if toremifene passes through breast milk. Therefore, if you are breastfeeding or plan to start, discuss this with your healthcare provider prior to taking the drug (see Fareston and Breastfeeding).