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Tamoxifen

Uses|Precautions & warnings|Side effects|Interactions|Dosage

Uses

What is tamoxifen used for?

Tamoxifen is part of a class of drugs known as antineoplastics, specifically an estrogen inhibitor used in hormonal therapy. Antineoplastics are used to treat various types of cancer. As an estrogen antagonist or inhibitor, tamoxifen works by binding to receptors on the target tissues, including tumors, which reduces DNA synthesis and the effects of estrogen.

Tamoxifen is indicated to treat the following conditions:

  • Breast cancer
  • Female infertility

How should I take tamoxifen?

Tamoxifen is available as an oral tablet. The oral tablet should be taken by mouth without chewing or crushing it. It can be taken with or without food, followed by a glass of water.

How do I store tamoxifen?

This drug should be stored at room temperature (20-25°C) and be protected from light and moisture. Do not freeze this product. Always check the label before using this product. For safety, keep out of the reach of children and pets.

Do not use if the printed expiration date has passed, the product seal has been broken, or the product has changed in color, odor, or consistency.

Do not dispose of this product by pouring it down the drain, toilet, or into the environment. Ask your pharmacist regarding the proper way and location of disposal.

Precautions & warnings

What should I know before using tamoxifen?

While estrogen inhibitors such as tamoxifen are used to treat and prevent breast cancer, it may increase the risk of other cancers, particularly endometrial and ovarian cancers. It can also increase the risk of embolisms and stroke.

Before using this medication, inform your doctor if:

  • You have ever had an allergic reaction to this medication
  • You have a history of allergy to other medications, food, or other substances
  • You are taking other medications
  • You have underlying health conditions
  • You are a tobacco user

Is it safe during pregnancy or breastfeeding?

This drug is a pregnancy category D drug. There is positive evidence that indicates that this drug can cause birth defects or fetal harm. This drug should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus, as determined by your doctor.

This drug may be excreted in breast milk. This drug should be used while breastfeeding only if the potential benefit justifies the potential risk to the child, as determined by your doctor.

Side effects

What side effects can occur when using tamoxifen?

All drugs have the potential to elicit side effects even with normal use. Many side effects are dose-related and will resolve when it is adjusted or at the end of therapy.

Potential side effects while using this drug include:

  • Hot flashes
  • Gastrointestinal disturbances
  • Nausea
  • Fluid retention
  • Vaginal discharge and bleeding
  • Pruritus vulvae
  • Dry skin
  • Rashes
  • Hair loss (alopecia)
  • Headache
  • Depression
  • Muscle cramps
  • Transient thrombocytopenia
  • Thromboembolism (blood clots)
  • Endometrial changes
  • Uterine fibroids
  • Blurred vision
  • Hepatitis

Rare, serious adverse reactions:

  • Stroke
  • Pulmonary embolism
  • Uterine sarcoma
  • Endometrial cancer

You may experience some, none, or other side effects not mentioned above. If you experience serious adverse reactions, you must stop taking the drug immediately. If you have any concerns about a side effect or it becomes bothersome, consult your doctor or pharmacist.

Interactions

What drugs may interact with tamoxifen?

This drug may interact with other medications. To avoid any potential drug interactions, you should keep a list of all the drugs you are using (including prescription drugs, nonprescription drugs, and herbal products) and share it with your doctor and pharmacist.

Known drugs and their interactions with medication include:

  • Bromocriptine
    • Increased dopaminergic effect of this drug
  • Cytotoxic agents
    • Increased risk of thromboembolic events
  • Platelet aggregation inhibitors
    • Increased risk of bleeding
  • Estrogen-containing medications (e.g. combination oral contraceptive pills)
    • Decreased efficacy of estrogen
  • CYP3A4 inducers
    • Reduced plasma levels of tamoxifen
  • CYP2D6 inhibitors
    • Reduced plasma levels of tamoxifen
  • CYP3A4 inhibitors
    • Increased plasma levels of tamoxifen
  • Coumarin-type anticoagulants
    • Increased anticoagulant effects (potentially fatal)

If you experience an adverse drug interaction, stop taking this drug and continue taking your other medication. Inform your doctor immediately to reevaluate your treatment plan. Your dose may need to be adjusted, substituted with another drug, or discontinue using the drug.

Does food or alcohol interact with tamoxifen?

This drug can be taken with or without meals, as there are no notable interactions. There are no notable interactions with alcohol with this drug, though it should be avoided or minimized.

Inform your doctor or pharmacist if you have any concerns regarding food-drug interactions.

What health conditions may interact with tamoxifen?

This drug should be taken with caution if you have any of the following conditions or risk factors:

  • CYP2D6 intermediate and poor metabolizers
  • History of deep vein thrombosis (DVT)
  • History of thromboembolic events
  • Leucopenia
  • Thrombocytopenia
  • Hyperlipidemia

Inform your doctor or pharmacist if you have any concerns regarding specific health conditions.

Dosage

The information provided is not a substitute for any medical advice. You should ALWAYS consult with your doctor or pharmacist before using tamoxifen.

What is the dose of tamoxifen for an adult?

To treat breast cancer

  • Take 20 mg once per day as a single dose or in 2 divided doses.
  • Maximum dose per day: 40 mg

To reduce the risk of breast cancer in high-risk women

  • Take 20 mg once a day for 5 years.

To treat anovulatory infertility

  • Take 20 mg once a day on days 2 to 5 of the menstrual cycle, increasing the dose if necessary, in the following cycles.
  • Maximum daily dose: 80 mg
  • For women with irregular periods: the initial course may begin on any day and a second course may start 45 days later.

What is the dose of tamoxifen for a child?

The recommended dose for pediatric patients has not been established. Ask your doctor or pharmacist for available substitutes and more information on this drug.

How is tamoxifen available?

This drug is available in the following brands, dosage forms, and strengths:

  • Gyraxen film-coated tablet 20 mg
  • Nolvadex-D tablet 20 mg
  • Tamoxen film-coated tablet 20 mg
  • Xifen tablet 20 mg

What should I do in case of an emergency or overdose?

In case of an emergency or an overdose, call your local emergency services or go to your nearest emergency room. Symptoms of overdose may include:

  • Neurotoxicity
    • Gait disorders
    • Hyperreflexia
    • Tremor
    • Dizziness
  • Changes in ECG reading
    • QT prolongation

What should I do if I miss a dose?

If you miss a dose of this drug, take it as soon as possible. However, if it is almost time for your next dose, skip the missed dose and take your regular dose as scheduled. Do not take a double dose.

Hello Health Group does not provide medical advice, diagnosis or treatment.

Sources

Tamoxifen. https://www.mims.com/philippines/drug/info/tamoxifen?mtype=generic. Accessed July 21, 2020

Nolvadex. https://www.nps.org.au/medicine-finder/nolvadex-d-tablets. Accessed July 21, 2020

Systemic antineoplastic therapy. https://www.msdmanuals.com/professional/hematology-and-oncology/principles-of-cancer-therapy/systemic-antineoplastic-therapy. Accessed July 21, 2020

 

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Medically reviewed by Stephanie Nicole Nera, RPh, PharmD
Written by Stephanie Nicole Nera, RPh, PharmD
Updated Jul 31, 2020
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