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Tamoxifen: Effect, areas of application, side effects

by Josephine Andrews
Published: Last Updated on 200 views

Tamoxifen is used in the treatment of breast cancer. It acts specifically on the docking sites of female sex hormones and can thus inhibit the growth of hormone-dependent tumors. Compared to other drugs used in cancer treatment, tamoxifen has a clear potential for side effects. It is therefore used particularly frequently in the treatment of breast cancer. Here you can read everything you need to know about the effects of tamoxifen, side effects and application.

This is how tamoxifen works

Tamoxifen is what is known as a Selective Estrogen Receptor Modulator (SERM). This means its anti-estrogen effect is cell and tissue specific.

For example, tamoxifen inhibits the action of estrogen (antagonistic) in breast tissue, while it acts as an agonist in the uterus , bones or lipid metabolism.

The endogenous female hormone estrogen (also: estrogen) not only determines the woman’s menstrual cycle, but also has other tasks in the body. Among other things, it ensures strong bones (a lack of estrogen can lead to osteoporosis ) and stimulates the immune system.

If estrogens are released in the body, they reach the target tissue via the bloodstream. Once there, they specifically influence the target cell and can, among other things, stimulate cell growth.

If a cell has many docking sites (receptors) for estrogens, it is particularly sensitive to the hormone. An increased number of estrogen receptors is found in a large proportion of breast tumors.

The already degenerated cells are stimulated by the natural estrogen to continue growing and dividing, i.e. multiplying, which causes the tumor to grow uncontrollably.

Tamoxifen and especially its metabolite hydroxytamoxifen can bind to estrogen receptors without stimulating cell division and proliferation in breast tissue. As a result, the existing receptors are blocked and can no longer be activated by the natural estrogen.

intake, degradation and excretion

After ingestion, the active ingredient is well absorbed in the intestine and reaches its maximum blood level after four to seven hours. The metabolism, which mainly takes place in the liver , leads to much more effective degradation products.

These are then excreted primarily with the stool, but this takes some time. Half of the active ingredient is only broken down and excreted after about a week.

When is tamoxifen used?

The active ingredient tamoxifen is approved for the treatment of hormone-dependent breast tumors. It can be used as a support after primary treatment for breast cancer or for breast cancer that has already formed secondary tumors (metastases).

The application usually takes place over a longer period of time. For example, if tamoxifen is used adjuvantly (to reduce the risk of recurrence), it is usually taken for five to ten years.

How Tamoxifen is used

The active ingredient is administered in the form of tablets. The usual tamoxifen dosage is twenty milligrams per day, but can be increased to up to forty milligrams if necessary. It is taken with a meal to reduce side effects such as nausea.

What are the side effects of tamoxifen?

Side effects seen in more than one in ten women treated include nausea, skin rash, fluid retention, vaginal discharge and bleeding, cycle changes and menopausal symptoms such as hot flashes and fatigue.

Every hundredth to tenth patient experiences drowsiness, headaches , blurred vision, vomiting, diarrhea , constipation , hair loss , hypersensitivity reactions, muscle pain, calf cramps, blood clots, temporary anemia and itching on the genitals.

A change in laboratory values ​​(elevated blood lipid values, changed liver enzyme values) can occur as a further side effect. Since tamoxifen has an estrogen agonistic effect in the uterus, it can promote the rate of cell division there and thus the formation of polyps (growths in the mucous membrane) or carcinomas.

Have unclear vaginal bleeding under tamoxifen therapy immediately clarified by a doctor!

What should be considered when taking Tamoxifen?

Contraindications

Tamoxifen must not be taken during pregnancy or while breastfeeding.

interactions

Therapy with tamoxifen is intended to reduce the effect of the body’s own estrogen. An additional supply of estrogen in the form of hormonal contraceptives (e.g. “the pill ”) would not make sense and should therefore be avoided.

Tamoxifen affects blood clotting by reducing the number of platelets in the blood. If anticoagulant medication is also given, the anticoagulant effect can be increased.

Examples of such “anticoagulants” include acetylsalicylic acid and other antiplatelet agents, as well as coumarin-type anticoagulants such as warfarin and phenprocoumon .

Tamoxifen is converted to the more active form by certain liver enzymes. Drugs that inhibit these enzymes or promote their activity can thereby affect the metabolism and thus the effectiveness of the cancer drug.

For example, antidepressants from the group of selective serotonin reuptake inhibitors (SSRIs, such as paroxetine and fluoxetine ) and also the antidepressant bupropion can reduce the effectiveness of tamoxifen through enzyme inhibition. The simultaneous use of such medicinal substances should therefore be avoided as far as possible.

age restriction

Tamoxifen is not approved for children and adolescents under the age of 18.

pregnancy and breast feeding period

Since there is little data on the use of tamoxifen during pregnancy and lactation, the active ingredient must not be taken during this time. In animal studies, taking tamoxifen caused harm to the unborn child.

How to get medication with tamoxifen

Preparations containing tamoxifen can be purchased in pharmacies in Germany, Austria and Switzerland with a prescription.

Since when is tamoxifen known?

As early as the late 1950s, pharmaceutical companies were actively researching antiestrogens (ie drugs that inhibit the action of estrogen) as an effective form of birth control. In doing so, Dr. Dora Richardson in 1966 the active ingredient tamoxifen.

However, this was not suitable for contraception, which is why it was forgotten again at first. It was later discovered that estrogens can also accelerate the growth of breast cancer.

As a result, a clinical trial of tamoxifen was started in 1971 at Christie Hospital in Manchester, one of the largest cancer hospitals in Europe. Because of the positive study results, tamoxifen was marketed in 1973 for the treatment of late-stage breast cancer. 

More interesting facts about tamoxifen

Tamoxifen is abused by male athletes as a doping agent. It increases testosterone levels, which stimulates muscle growth. In addition, tamoxifen prevents a common side effect of anabolic steroids, the so-called “man boobs” ( gynaecomastia ). 

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