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Tamoxifen

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

Tamoxifen is part of a class of drugs known as antineoplastics, specifically an estrogen inhibitor. Antineoplastics are drugs that fight cancer. As an estrogen antagonist or inhibitor, tamoxifen binds to receptors on the target tissues, including tumors, which reduces DNA synthesis and the effects of estrogen.

tamoxifen
breast cancer

Uses

What is tamoxifen used for?

It 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 product is best stored at room temperature away from direct light and moisture. To prevent drug damage, you should not store it in the bathroom or the freezer.

There may be different brands of this drug that may have different storage needs. So, it is important to always check the product package for instructions on storage, or ask your pharmacist. For safety, you should keep all medicines away from children and pets.

You should not flush this product down the toilet or pour them into a drain unless instructed to do so. Additionally, it is important to properly discard this product when it is expired or no longer needed. Consult your pharmacist for more details about how to safely discard your product.

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 drug, tell your doctor if you are/have:

  • Pregnant or breastfeeding.
  • Taking any other medicines. This includes any prescription, OTC, and herbal remedies.
  • An allergy to any of the ingredients of this product.
  • An active smoker.
  • Any other illnesses, disorders, or medical conditions.

Is it safe during pregnancy or breastfeeding?

There is positive evidence that this drug can cause birth defects or fetal harm. Therefore, it should not be used during pregnancy unless the benefits greatly outweigh the risks.

This medication is pregnancy risk category D according to the US Food and Drug Administration (FDA).

FDA pregnancy risk category reference below:

  • A=No risk
  • B=No risk in some studies
  • C=There may be some risk
  • D=Positive evidence of risk
  • X=Contraindicated
  • N=Unknown

Tamoxifen accumulates in breastmilk and can suppress lactation. Breastfeeding should be avoided while taking this drug.

Side effects

What side effects can occur when using tamoxifen?

Like all drugs, this product may have side effects. If they occur, side effects are generally mild and resolve once treatment is finished or the dose is lowered. Some reported side effects include:

  • Hot flashes
  • Gastrointestinal disturbances
  • Nausea
  • Fluid retention
  • Vaginal discharge and bleeding
  • Vulvar itching
  • 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

However, not everyone experiences these side effects. In addition, some people may experience other side effects. So, if you have any concerns about a side effect, please consult your doctor or pharmacist.

Interactions

What drugs may interact with tamoxifen?

This medication may interact with other drugs that you are currently taking, which can change how your drug works or increase your risk for serious side effects.

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.

Drugs with known interactions:

  • Bromocriptine
  • Cytotoxic agents
  • Antiplatelet drugs (e.g. aspirin)
  • Estrogen-containing medications (e.g. combination oral contraceptive pills)
  • CYP450 enzyme inducers and inhibitors
  • Coumarin-type anticoagulants

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. Approaches include dose adjustment, drug substitution, or ending therapy.

Does food or alcohol interact with tamoxifen?

This drug may interact with food or alcohol by altering the way the drug works or increase the risk for serious side effects. Please discuss with your doctor or pharmacist any potential food or alcohol interactions before using this drug.

What health conditions may interact with tamoxifen?

This drug may interact with underlying conditions. This interaction may worsen your health condition or alter the way the drug works. Therefore, it is important to always let your doctor and pharmacist know all the health conditions you currently have, especially:

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

Dosage

The information provided is not a substitute for any medical advice. Therefore, you should always consult with your doctor or pharmacist before using any medication.

What is the dose 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 is 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 is 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 for a child?

There is no established pediatric dose. It may be unsafe for your child. It is always important to fully understand the safety of the drug before using. Please consult with your doctor or pharmacist for more information.

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 the nearest emergency room.

What should I do if I miss a dose?

If you miss a dose, 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 June 16, 2021

Tamoxifen https://www.breastcancer.org/treatment/hormonal/serms/tamoxifen Accessed June 16, 2021

Tamoxifen and Breast Cancer https://my.clevelandclinic.org/health/drugs/9785-tamoxifen Accessed June 16, 2021

Tamoxifen (Oral Route) https://www.mayoclinic.org/drugs-supplements/tamoxifen-oral-route/description/drg-20066208 Accessed June 16, 2021

Drugs and Lactation Database – Tamoxifen https://www.ncbi.nlm.nih.gov/books/NBK501106/ Accessed June 16, 2021

Tamoxifen. Lexi-Drugs. Lexicomp. Wolters Kluwer Health, Inc. Riverwoods, IL. Accessed June 16, 2021. http://online.lexi.com

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Written by Stephanie Nicole Nera, RPh, PharmD Updated Jun 16
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